Catch exceptions in project list generator

If the generator that produces per-project worker arguments raises an
exception it triggers python bug http://bugs.python.org/issue8296.
Rewrite the generator expression as a generator function, and catch
Exceptions and KeyboardInterrupts to end the iteration.

Also add a pool worker initializer to disable SIGINT to prevent
KeyboardInterrupts inside multiprocessing.Pool in the worker threads
causing the same problem.

Fixes easy-to-reproduce hangs when hitting ctrl-c during
repo forall -c echo

Change-Id: Ie4a65b3e1e07a64ed6bb6ff20f3912c4326718ca
1 file changed