Allow users to pass "headers" and "method" argument to the get_response_object
utility method.
Use assertEqual instead of the deprecated assertEquals

Closes #375

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Allow passing `credential_file` to be used in the GCEConnection

Closes #359

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Bump versions for 0.16.0 release.
LIBCLOUD-625: fixing merge conflicts