Stop using config option sqlite_db
Stop using config option sqlite_db

Config option sqlite_db is deprecated
in 0a1bae9859079fb21a03716be947c5f1da6db0a2, and now we use database
with sqlite in memory mode[1] like this: CONF.set_default('connection',
"sqlite://", group='database')so don't need use config option sqlite_db
any more and override its default value.

[1]http://docs.sqlalchemy.org/en/rel_1_0/core/engines.html#sqlite

Change-Id: Ic7ef914757b0613ea7209a893fad126b5a6c00a1

ramineni/my_congress,ramineni/my_congress,openstack/congress,openstack/congress,ramineni/my_congress,ramineni/my_congress