Use constant for project key.

Author: daspecster

gcloud/_helpers.py

@@ -184,15 +184,16 @@ def _default_service_project_id():
     :rtype: str or ``NoneType``
     :returns: Project-ID from ``gcloud info`` else ``None``
     """
+    PROJECT_KEY = 'project = '
     command = subprocess.Popen(['gcloud', 'config', 'list', 'project'],
                                stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                shell=True)
     gcloud_project_conf = command.communicate()[0].decode('utf-8')
     gcloud_project_conf = gcloud_project_conf.split('\n')
 
     for key in gcloud_project_conf:
-        if key.startswith('project = '):
-            return key[10:]
+        if key.startswith(PROJECT_KEY):
+            return key[len(PROJECT_KEY):]
 
     return None