Use memory mode for sqlite in db test
Use memory mode for sqlite in db test

Config option sqlite_db is deprecated in
0a1bae9859079fb21a03716be947c5f1da6db0a2, and deprecate argumentsqlite_db in method set_defaults in
https://review.openstack.org/#/c/350945/, should use config option
connection instead. For watcher, we test database with sqlite in memory
mode [1] as below:

cfg.CONF.set_override("connection", "sqlite://",
                      group="database", enforce_type=True)

and don't use config option sqlite_db, so remove unused code.

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

Change-Id: I9b1f995e1b7004bcfe6c5a854c2f83b24e5bfb56

openstack/watcher,openstack/watcher,stackforge/watcher,stackforge/watcher