Added more checks to the configure script

Added checks which look for the 'katello' user and for the 'katello'
group.
Made the configure script more robust

Ensured the '/etc/katello' is created if it does not exist.
Fixed invocation of katello-configure from the git checkout

Made possible to invoke katello-configure straight from a git checkout.
This was no longer possible since the layout of the git repository has
been changed over the time breaking some require statement.

Because of the same reason puppet was looking for modules and libs into
the wrong paths.
katello configure: fixed behaviour when run from git checkout

Took in consideration the default_answers file contained into the
git repository when the configure script is invoked from the git
checkout.