Allowing pyOpenSSL import to fail for GAE.

Fixes #1445.

Author: dhermes

gcloud/credentials.py

@@ -19,7 +19,12 @@
 import six
 from six.moves.urllib.parse import urlencode  # pylint: disable=F0401
 
-from OpenSSL import crypto
+try:
+    from OpenSSL import crypto
+except ImportError:
+    # pyOpenSSL can't be installed on App Engine, but it will not
+    # be needed there since app_identity is used.
+    crypto = None
 
 from oauth2client import client
 from oauth2client.client import _get_application_default_credential_from_file