Use valid hostnames in $wgLBFactoryConf

Use 'deployment-db1' instead of 'db1' as the hostname in
$wgLBFactoryConf so that `wfGetLB()->getServerName(0)` will return
a value that can be used by `mysql` to connect via the
/usr/local/bin/sql wrapper script.

Bug: 63803
Change-Id: I081125f48c8118c41526b42c5706f5a3650cf83c