Try pulling from builds.puppetlabs.lan to retrieve

Retrieving directly from the distribution server requires access to it, which
many don't have. This commit updates the retrieve task to first try to wget
the packages from the distribution server's host, and if that fails then fall
back to rsyncing.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Merge pull request #117 from MosesMendoza/maint/master/switch_to_wget_retrieve

Try pulling from builds.puppetlabs.lan to retrieve