Default to system CA bundle if no CA certificate is provided

If no CA certificate is provided to be used for validation then
fall back to the system-wide CA bundle as presented by
python-requests.

Change-Id: I05206a868150d4b62b6f1b833310eb9b86b7c4f8
Closes-bug: #1362179
Skip non-base properties in patch method

It's currently impossible to update properties which are defined in
image schema and which are not a base image property. Proposed fix skips
every non-base property when building a json patch, that is used to
update image properties through glance API.

Change-Id: I3b35cef379fcf437715e2966f9a0d25c1b4e4016
Closes-Bug: #1371559
Merge "Skip non-base properties in patch method"
Remove network_utils

Use oslo.utils instead

Change-Id: I4830b13794db5570e7dde4a897a7396065028e37
Merge "Default to system CA bundle if no CA certificate is provided"
Merge "Remove network_utils"