Fix Neutron flavor framework

Fix Neutron flavor framework

Make flavor service profile store actual driver instead of
hardcoded dummy driver.  Ensure service type on flavor persisted.

Raise ServiceProfileDriverNotFound if non-empty driver is not part
of ServiceTypeManager providers.

Raise ServiceProfileEmpty if profile has neither a driver nor
any metainfo.

Raise InvalidFlavorServiceType if invalid service type passed.

Show flavors associated with a profile, not just profiles associated
with a flavor, to ease diagnosis when ServiceProfileInUse raised.

Create method to extract provider given a flavor for use with
neutron-lbaas plus tests.

Ensure various boolean forms accepted for enabled flag.

To enable in DevStack, add to local.conf:
enable_plugin neutron https://git.openstack.org/openstack/neutron
enable_service q-flavors

Add associated unit tests. Fix tempest api test that used invalid
LOADBALANCERS service type.

Change-Id: I5c22ab655a8e2a2e586c10eae9de9b72db49755f
Implements: blueprint neutron-flavor-framework