cmd/bash is confusingly named/used

[imjasonh]

Expected Behavior

Image named bash executes provided args using the Bash shell.

Actual Behavior

It invokes the args with sh -c (Bourne shell), not Bash. The image is based on busybox, whose default shell is ash. Busybox doesn't even include Bash:

$ docker run busybox bash
docker: Error response from daemon: OCI runtime create failed: container_linux.go:344: starting container process caused "exec: \"bash\": executable file not found in $PATH": unknown.

Additional Info

Since the details of the bash image are intended to be an internal implementation detail, one solution is to simply rename the image to something more correctly descriptive. Nothing that uses the image actually relies on Bash behavior, so we could just rename it to sh.

Also, provided examples for using the image are incorrect. Passing multiple string args will result in only the first one being interpreted, further args will be ignored:

$ docker run $KO_DOCKER_REPO/github.com/tektoncd/pipeline/cmd/bash -args echo hello world
{"level":"info","ts":1571672349.923307,"logger":"fallback-logger","caller":"bash/main.go:64","msg":"Successfully executed command \"sh -c echo\"; output \n"}