Fixes messages logged on Glance plugin retries

Retry logic is now being used for both upload_vhd and download_vhd,
but nova/virt/xenapi/client/session.py still had 'upload_vhd'
hardcoded in its logged messages. This change causes it to accept the
function being used as an argument and display that.

Fixes-Bug: #1265054
Change-Id: I6203aef81960078f92fa7839e47ee1c84df95745
Add tests for remaining expected conductor exceptions

This fills out coverage of our expected exceptions on conductor
methods, which helps ensure we don't drop an expected exception
class during a refactor.

Change-Id: Iacd5315d47ad97c8aad43d2f6a23674529775e63
Update docs to reflect new default filters

Server group scheduler filters were added to the default set of
scheduler filters.  Update the docs to reflect the updated defaults.

Change-Id: I614cf83e419c93038fc4ed7287ec743cedb4860e
Related-bug: #1303983
Merge "Update docs to reflect new default filters"
Merge "Fixes messages logged on Glance plugin retries"
Merge "Add tests for remaining expected conductor exceptions"