After support for multiple databases were added to devstack,
configure tempest would not work with update_database() in
localrc.
This sources lib/database before localrc is loaded so that
update_database is defined. Also, COMPUTE_DB_URI is now
replaced by BASE_SQL_CONN from lib/database.
Change-Id: Ifd791e5732898a661cc1237839bd18cef2f36f60
Signed-off-by: Matthew Treinish <treinish@linux.vnet.ibm.com>