Use bash

[tusharpm]

The intent is to (help) address the issue travis-ci/apt-package-safelist#3946 I raised earlier among others. The message pointed to a missing source repository for the given package (mine was g++-6).
On further debugging, I found out that without the -s flag apt-add-repository adds the deb-src entry under /etc/apt/sources.list.d/,,, commented, unavailable for the subsequent apt commands.

In this PR:

• Modified the ruby script to enable adding the source repository along with the binary repository
• Modified the bash script to perform the same action(s) locally (instead of invoking ruby) - use jq for JSON.

[grooverdan]

Nice work.

It looks like this will prevent the selecting a very different source repo like I encountered in travis-ci/apt-package-safelist/issues/4071 (clang-5.0 became a clang-3.5 request).

Ref: its corresponding build https://travis-ci.org/travis-ci/apt-whitelist-checker/builds/219882514#L789

@BanzaiMan, willing to give this pull request a try?

[tusharpm]

Happy to help.
Although, I'm not sure this will be accepted in its current form - it can look like too many changes to solve a simple problem. I had made it two commits for that reason, the first one addressing the problem in the Ruby script itself. The second one is a simplification as it performs the same actions from bash.
The maintainers can optionally cp either commit (or both) as that would have the same result. Alternatively, I can open a different PR with just the flag added in the Ruby script (in two places without my change).
@grooverdan @BanzaiMan Please let me know how to proceed.

[BanzaiMan]

Sorry for the delay. If add_sources.rb is being replaced with the bash equivalent, it is best to remove the file altogether.

[tusharpm]

Just a heads-up: I saw another Ruby script doing something similar in another repo - https://github.com/travis-ci/apt-source-whitelist/blob/master/add_all.rb.
The same change might be required there as well.