Removes os-instance-usage-audit-log from the V3 API

The extension pre-dates ceilometer and equivalent
functionality is now much better managed using
ceilometer. So we're removing this before the V3 API
is officially released.

Partially implements blueprint v3-api-remove-extensions

Change-Id: I9b7892346a4ad7c54a903cfcbcb97156dfc8c734
Fix compute_node_update() compatibility with older clients

A recent change changed the format of the data passed to conductor's
compute_node_update() method. The 'stats' element of 'values' was
changed from a dict to a JSON-encoded string. When older clients
call this method with a dict, the newer conductor puts the actual
dict in the SQL instead of a string, which breaks.

Change-Id: Ida1ad76752b1944f33c1aa9436ce36790705d6a5
Closes-bug: 1280034
Merge "Removes os-instance-usage-audit-log from the V3 API"
Merge "Fix compute_node_update() compatibility with older clients"