spacemanager: Use HikariCP

To gain experience with an alternative to BoneCP, this patch
switches space manager to HikariCP. I chose space manager because
the configuration parameters for the connection pool where new
in 2.8 and thus they are easy to change now.

Introduces these new properties:

spacemanager.db.connections.max
spacemanager.db.connections.min

Drops these unpublished properties:

spacemanager.db.connections.partition-count
spacemanager.db.connections.max-per-partition
spacemanager.db.connections.min-per-partition

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/6475/