Update python-openstackclient-base and python-glanceclient

We update python-glanceclient to upstream version 0.5.1 (same
as in current epel) and fix image downloading. To do the latter we
change the way we make image downloading work: instead of patching
python-glanceclient we provide compatibility method in
openstackclient_base.

Change-Id: I23e78379b7a7cf594d884eab6a86021c9419c10f