rdbms: set the schema in the LBFactory local domain

rdbms: set the schema in the LBFactory local domain

Also, enforce that new DB connection use the domain
schema as is the case with the DB name and table prefix.

The code worked previously since the local domain did not override
the schema in the server configuration arrays, so it happened not
to clobber the domain schema.

Lastly, fix unit test fatal in LBFactorySingle::forEachLB() when
called during LBFactorySingle::_destruct().

Change-Id: Ia9ddef0f21591d0c8b15f2947cd61569e3fec7a0