[engine] bug fix: ensure we catch all exceptions in subprocess

Review Request #3656 - Created April 7, 2016 and submitted

Peiyu Wang
3149, 3155
kwlzn, patricklaw, stuhood

We intended to catch all subprocesses exceptions, for example the test case
EngineTest.test_multiprocess_unpickleable checks SerializationError, but some
later added code wasn't protected, including line #159 that caused
https://github.com/pantsbuild/pants/issues/3149 test to hang.

This review fixes this by moving everything into the same try block.

This review does not fix the root cause of https://github.com/pantsbuild/pants/issues/3149
but next time it happens the subprocess won't die and will report the
exception back to the engine.

https://travis-ci.org/peiyuwang/pants/builds/121229553 passed.

Kris Wilson
Peiyu Wang
Review request changed

Status: Closed (submitted)

Change Summary:

submitted as f18ce8f4131a85be845ec3becf6d164cfcbdb8bf