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
Make is_neutron() thread-safe

The utils method is_neutron() was not thread safe and could have returned the
wrong value if two greenthreads called it at the same time.  Specifically, a
greenthread switch could occur when the import is being done.  At that point, it
looks like the check has already been completed, but the result has not yet been
recorded.

Closes-bug: #1274992
Change-Id: I5a6eedaeb4c0deee4b31509946ae5daedf98389d
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"
Merge "Make is_neutron() thread-safe"