Bugfix for savings settings when configMap exists but does not have any data

[stefansundin]

Initialize cm.Data if it is nil. This happens if the configMap exists but does not have any data in it, and in this case it was not possible to update the dashboard settings.

For example, the configMap provided here causes the bug: https://github.com/kubernetes/kubernetes/blob/0928bb4c01f6e7ed7c8b990693dd9ea27873def7/cluster/addons/dashboard/dashboard-configmap.yaml

When trying to save, this is the stacktrace that was returned. It does not show up in the UI though, had to find it by using the chrome developer tools.

[restful] recover from panic situation: - assignment to entry in nil map
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/runtime/asm_amd64.s:514
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/runtime/panic.go:489
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/runtime/hashmap.go:487
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/settings/manager.go:108
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/settings/handler.go:92
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/settings/handler.go:43
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/container.go:244
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/filter.go:21
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/handler/filter.go:46
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/filter.go:19
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/handler/filter.go:121
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/filter.go:19
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/handler/filter.go:94
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/filter.go:19
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/src/app/backend/handler/filter.go:58
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/filter.go:19
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/container.go:246
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/container.go:95
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/server.go:1942
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/server.go:2238
    /home/travis/build/kubernetes/dashboard/.tmp/backend/src/github.com/kubernetes/dashboard/vendor/github.com/emicklei/go-restful/container.go:264
    <autogenerated>:32
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/server.go:2238
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/server.go:2568
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/server.go:3088
    <autogenerated>:312
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/h2_bundle.go:4331
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/net/http/h2_bundle.go:4611
    /home/travis/.gimme/versions/go1.8.3.linux.amd64/src/runtime/asm_amd64.s:2197

Fixes #3149

[maciaszczykm]

Thanks! Tests have crashed. You can push commit again with --amend to restart them.

/lgtm

[codecov]

Codecov Report

Merging #3280 into master will increase coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #3280      +/-   ##
==========================================
+ Coverage    54.6%   54.61%   +0.01%     
==========================================
  Files         565      565              
  Lines       12424    12427       +3     
==========================================
+ Hits         6784     6787       +3     
+ Misses       5380     5378       -2     
- Partials      260      262       +2

Impacted Files	Coverage Δ
src/app/backend/settings/manager.go	52.63% <0%> (-2.93%)	⬇️
src/app/backend/sync/secret.go	69.49% <0%> (+2.54%)	⬆️

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[stefansundin]

@maciaszczykm I rebased and that fixed the travis tests, but I don't know what is going on with codecov.

[maciaszczykm]

It's ok.

/lgtm

[jeefy]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jeefy, maciaszczykm, stefansundin

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