Reduce verbosity of build tool/dep fetching. Mainly to declutter Kokoro logs.

The git fetching progress in stderr doesn't seem particularly useful even in an
interactive session. Made the git invocation use --quiet unconditionally.

Ninja currently still prints a line per build step, which is quite spammy, but
there's no simple flag to reduce verbosity, and everything (including errors)
gets funneled into stdout. One hacky approach I'm considering is:
NINJA_STATUS="[ninja progress: %f/%t] " tools/ninja -C ${OUT_PATH} | \
  awk '$1 !~ /^\[ninja/ || NR % 100 == 1

Which will print every 100th line of progress, and anything that isn't a
progress statement (e.g. errors). But am not sure it catches all interesting
output, WDYT?

Change-Id: I5e29b2e91996cbefb8f686bd66da23e19e9f70dc
diff --git a/tools/install-build-deps b/tools/install-build-deps
index 73ab0d7..e886ebc 100755
--- a/tools/install-build-deps
+++ b/tools/install-build-deps
@@ -342,7 +342,7 @@
   logging.info('Fetching %s @ %s into %s', git_url, revision, path)
   subprocess.check_call(['git', 'init', path], cwd=path)
   subprocess.check_call(
-    ['git', 'fetch', '--depth', '1', git_url, revision], cwd=path)
+    ['git', 'fetch', '--quiet', '--depth', '1', git_url, revision], cwd=path)
   subprocess.check_call(['git', 'checkout', revision, '--quiet'], cwd=path)
   assert(IsGitRepoCheckoutOutAtRevision(path, revision))