Adding feature for custom up- and downscripts

Added a new manifest, ucarp::scripts, along with two new class parameters, to allow for customizing upscripts and downscripts.  In particular, this lets us start/stop services on failover events.

As far as filesystem locations go, none of this is set in stone: all I care about is that we have working code.  We do need to be a bit careful about the default Red Hat initscript: at least when installed from EPEL, the upscript/downscript location is hard-coded to /usr/libexec/ucarp.  We could potentially expose a scriptDir parameter to work around this.

Also worth considering: what if Red Hat changes the default up/downscripts?  We're creating them from template; we may want to leave them alone altogether if no script parameters are passed.