meter: move the module to osgi bundle

Even though usage should be part of Killbill core, the metering piece
can be extracted as a plugin (metering could be handled in an external
system).

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
healthchecks: don't scan full tables

Make sure to only return 1 row from the tables. That should be enough to
check the connection to the db is working and the table is present.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>