gerrit: catch GoB exceptions and present a pretty message
gerrit: catch GoB exceptions and present a pretty message

Rather than dumping the traceback when we get a GoB exception, catch it
and show the existing pretty die message.  If people want to debug the
issue further, they can use --debug.

BUG=chromium:327217
TEST=`gerrit inspect 24624` w/empty .netrc no longer shows traceback

Change-Id: I90a8ec760a67fd799beb9e3d37de398f5fc3d849
Reviewed-on: https://chromium-review.googlesource.com/185592
Reviewed-by: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Commit-Queue: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite