(SERVER-87) Add upgrade behavior to pre_suite.

When PUPPETSERVER_INSTALL_MODE=upgrade is set in the environment from which
beaker is run, the pre_suite will first install the latest version of puppet and
puppetserver from the official puppetlabs release repository, run the
initialize_ssl, procedure, then install puppetserver from the development
repository.

Note that initialize_ssl will only happen once--immediately after the initial
install. There will be no initialize_ssl after the upgrade install.
(SERVER-87) Actually install released puppetserver.
Merge pull request #252 from waynr/server-87

(SERVER-87) Add upgrade behavior to pre_suite.