ctdb-util: Rename db_wrap to tdb_wrap and make it a build subsystem

ctdb-util: Rename db_wrap to tdb_wrap and make it a build subsystem

This makes it consistent with Samba, to ease transition.

Update unit test code to link to with tdb_wrap instead of including
db_wrap.c.

There are some potential whitespace fixes in this commit that have
been ignored.  CTDB's lib/tdb_wrap will be deleted after the
transition to Samba's lib/tdb_wrap, so there's no point polishing it
too much.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>