Sign when shipping for PE

We say we're going to sign with the pe:jenkins:uber_ship, but then we actually
just don't. We should probably do that. This commit adds the
pl:jenkins:sign_all to the list.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Merge pull request #145 from MosesMendoza/sign_when_shipping_pe

Sign when shipping for PE