Define GIT_CURL_VERBOSE to monitor ls-remote usage

When calling gclient_sync_retry define GIT_CURL_VERBOSE. This shows
HTTP requests made. For tracking ls-remote usage, we want to count
"/info/refs".

Change-Id: If69a2042dc7941c2da81cdcf85d2c6c9259ff58a
diff --git a/gclient_sync_retry.py b/gclient_sync_retry.py
index 7588167..f8abced 100644
--- a/gclient_sync_retry.py
+++ b/gclient_sync_retry.py
@@ -37,6 +37,7 @@
 
   max_runs = 3
   fail_string = 'Failed to connect'
+  os.environ['GIT_CURL_VERBOSE'] = '1'
   for run in range(1, max_runs + 1):
     sys.stdout.write('Attempt %d\n' % run)
     p = subprocess.Popen(