Log if a quota_usages sync updates usage information

There's some periodic quota_usages syncing that can occur to help
correct any drift that may happen.  It would be useful to log when that
occurs as it may indicate an issue somewhere.

Change-Id: I5b90ab42059ae8ebd0c3890accafb98e70ed037e
Reserve 10 migrations for backports

Reserve 10 migrations so that we have the option of backporting fixes
that include a db migration to the stable/havana branch.  We did this
same thing to allow backports to stable/grizzly in
b52a2157bedba693c5da7dcb783b7a151769d6b1.

The choice of 10 migrations is just a magic number.  We haven't used any
of the 10 reserved for stable/grizzly backports, so 10 seems to be
enough.

Implements blueprint backportable-db-migrations-icehouse

Change-Id: I2c5f2e5a966cfffa4a3e54e17fde07a52295f658
Merge "Reserve 10 migrations for backports"
Merge "Log if a quota_usages sync updates usage information"