gerrit-util: Fix GCE check from behind proxy.

Setting HTTP_PROXY or HTTPS_PROXY environment variables will cause git cl
to fail.

The behavior of an unreachable server behind proxy is different from a direct
connection, it won't throw a httplib2.ServerNotFoundError error,
so catch httplib2.Httplib2Error instead.

Bug: 1050380
Change-Id: I32e2220483de1fd6222c7fd6063039fb86277ef0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2050947Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

gerrit_util.py

@@ -288,8 +288,7 @@ class GceAuthenticator(Authenticator):
     # Based on https://cloud.google.com/compute/docs/metadata#runninggce
     try:
       resp, _ = cls._get(cls._INFO_URL)
-    except (socket.error, httplib2.ServerNotFoundError,
-            httplib2.socks.HTTPError):
+    except (socket.error, httplib2.Httplib2Error):
       # Could not resolve URL.
       return False
     return resp.get('metadata-flavor') == 'Google'