Make sure /sbin is in $PATH during spacewalk-setup

Fixes the following error mentioned in /var/log/rhn/install_db.log :
/usr/bin/spacewalk-setup-postgresql: line 257: chkconfig: command not found
Don't continue when spacewalk-setup fails
Update to Spacewalk 2.1
make spacewalk_client_repo optional, support reregistration

introduced two new options to spacewalk::client

- force_registration: if set to yes, the client is going to reregister
  itself to the spacewalk server on the next run. use with care as this
  can result in the same system registered more than once on the server.

- use_spacewalk_client_repo: if spacewalk::client should configure the
  spacewalk client repository and exec setupSpacewalkClientRepo.

  when using a redhat satellite server, the client repo is not needed.
import rspec tests for client.pp
added stdlib to dependencies
documentation update for the force_registration option