Prevent WantReadError when using https

If the glance client is instantiated when the socket module has been
monkey patched requests to the server can yield a WantReadError because
the socket has been set to non-blocking but this is not being handled
correctly. When this is the case use eventlet's GreenConnection which
handles non-blocking sockets correctly.

Also, for now, add a required getsockopt method to GreenConnection.
This can be removed once the eventlet fix
(https://bitbucket.org/eventlet/eventlet/commits/609f230) lands.

Fixes bug 1157864.

Change-Id: I187b69f75b8bcfe16facd41e69b1cd0490dae605
Merge "Prevent WantReadError when using https"