srm: Replace custom DB connection pool with BoneCP

Among other things, BoneCP does statement caching - something
our custom pool didn't do.

Target: trunk
Require-notes: yes
Require-book: no
Acked-by: Dmitry Litvintsev <litvinse@fnal.gov>
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5951/