Don't rm repodata in pe ship, just update it

We currently rm the entire set of yum metadata with in the pe:ship task. This
commit updates this to use --update and not rm, which will be much faster.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Merge pull request #195 from MosesMendoza/maint/master/update_dont_delete_metadata

Don't rm repodata in pe ship, just update it