The quota driver ``ConfDriver`` was deprecated in Liberty release.
``NullQuotaDriver`` is created for testing although it could be used
in production if no quota enforcement is needed. However, because
the Quota engine is not plugable (is an extension always loaded), it
could be interesting to make it plugable as any other plugin.
This patch also creates a Quota engine driver API class that should be
used in any Quota engine driver. Currently it is used in the three
in-tree drivers implemented: ``NullQuotaDriver``, ``DbQuotaDriver``
and ``DbQuotaNoLockDriver``.
Change-Id: Ib4af80e18fac52b9f68f26c84a215415e63c2822
Closes-Bug: #1928211
ad31c58d60