16572 - deb pkg installs to a ruby-version independent dir

As newer debian/ubuntu releases default to ruby 1.9, mcollective-common
should install files to a version-independent directory.

/usr/lib/ruby/vendor_ruby/ has been in ruby's default path on debian at
least since lenny (2009).

This is a slight rework of #51 to adds the change noted by @haus to make the install action install to the same staging path as it will end up in.