Add init scripts and docs for Upstart and OpenRC

Expanding on @aitorpazos earlier commit of a systemd service file, here are some additional scripts and documentation updates to support Upstart and OpenRC.  Tested on Gentoo/OpenRC 0.12.4 and Ubuntu trusty/Upstart 1.12.1. 
Sure.  Also, I noticed overnight that the Gentoo ebuild for bitcoind has a nicer OpenRC init file that checks a few more things.  I'll merge in the good stuff from there too...