Pass --quiet flag to 'git cache exists'.
Pass --quiet flag to 'git cache exists'.

Without this flag, git_cache.py will print a message whenever a
--cache-dir argument contradicts the global cache setting in
$HOME/.gitconfig.

TBR=iannucci@chromium.org,hinoka@chromium.org
BUG=

Review URL: https://codereview.chromium.org/296263007

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@272451 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build