Add ability to set prefix for gerrit url

Update run_tests.sh

Change-Id: Id6339eb38584dcf0d31fc94c9d404feec26d6faa
Related-prod: #PROD-27651 (PROD:27651)
diff --git a/_modules/gerrit.py b/_modules/gerrit.py
index 4f66fd2..db2a118 100644
--- a/_modules/gerrit.py
+++ b/_modules/gerrit.py
@@ -456,11 +456,12 @@
     host = get('host', 'localhost')
     http_port = get('http_port', '8082')
     protocol = get('protocol', 'http')
+    url_prefix = get('url_prefix', '')
     username = get('user', 'admin')
     password = get('password', 'admin')
     auth_method = get('auth_method', 'digest')
 
-    url = protocol + "://" + str(host) + ':' + str(http_port)
+    url = protocol + "://" + str(host) + ':' + str(http_port) + str(url_prefix)
 
     if auth_method == 'digest':
         auth = requests.auth.HTTPDigestAuth(username, password)