gerrit: add a generic "search" command
gerrit: add a generic "search" command

This lets people perform any kind of search they want and makes
the "mine" command a simple alias.

BUG=chromium:384547
TEST=`gerrit mine` still works
TEST=ran some custom queries and compared output to the web interface

Change-Id: I0108ee66c06f2dc4ba9cfb1497af930cbb575fa7
Reviewed-on: https://chromium-review.googlesource.com/203808
Reviewed-by: Aviv Keshet <178e8ae417efbe404feca7ab4cb8f0ba8c109369@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

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