Add support for other operating systems besides Redhat/Debian

Prior to this commit, if you attempted to use the module to
manage postgres on any OS other than Redhat/Debian, there
was an explicit check for that, and a call to `fail`.

In reality, the OS family is only used to build up defaults
for various path and package names, which are all exposed
as parameters.  If the user is willing to explicitly pass
in all of those parameters, there's no reason we should
fail based on OS family.

This commit adds checks to the 'default' osfamily case
such that we now only fail if they're on a non-Redhat-or-Debian
system *and* they haven't explicitly passed in values for
all of the required parameters.