bazel: tidy up bin/bazel invocations a bit

[ParkMyCar]

Wrap the call to subprocess in a try-catch so when a Bazel build fails or is canceled we don't print the Python backtrace.

Motivation

Makes bin/bazel a little nicer.

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[def-]

What kind of side effects does it have that we continue running at this point? The command will also return 0 (success) now even when a failure happened. I'd suggest at least passing the error through and returning 1 from main, or alternatively catching the exception in main and returning the error there, without ever printing the python backtrace.