Include standard out/error output in exception output

The pre-commit hook context would only include output from standard
error when an exception occurred. Unfortunately, this sometimes leaves
out important information for debugging purposes.

Include both streams in the output to aid in debugging.

Change-Id: Ib38348174c983d7133721120c64af6cba8f0254e
Reviewed-on: http://gerrit.causes.com/42177
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>