Adding extra __environ__ for user agent.

Fixes #566.

gcloud/__init__.py

@@ -16,4 +16,32 @@
 
 from pkg_resources import get_distribution
 
+import httplib2
+import socket
+
+__environ__ = ''
+try:
+    from google import appengine
+    __environ__ = '-GAE'  # pragma: NO COVER
+except ImportError:
+    pass
+
+
 __version__ = get_distribution('gcloud').version
+
+
+if __environ__ == '':
+    RESPONSE = None
+    try:
+        RESPONSE, _ = httplib2.Http(timeout=0.1).request(
+            uri='http://169.254.169.254/computeMetadata/v1/project/project-id',
+            headers={'Metadata-Flavor': 'Google'})
+
+        if RESPONSE['status'] == '200':  # pragma: NO COVER
+            __environ__ = '-GCE'  # pragma: NO COVER
+    except socket.timeout:
+        pass
+    finally:
+        del RESPONSE
+else:  # pragma: NO COVER
+    pass  # pragma: NO COVER

gcloud/connection.py

@@ -32,7 +32,8 @@ class Connection(object):
     _EMPTY = object()
     """A pointer to represent an empty value for default arguments."""
 
-    USER_AGENT = "gcloud-python/{0}".format(gcloud.__version__)
+    USER_AGENT = "gcloud-python/{0}{1}".format(gcloud.__version__,
+                                               gcloud.__environ__)
     """The user agent for gcloud-python requests."""
 
     def __init__(self, credentials=None):