Remove unneeded ||= and correct uber dependencies

The ||= for assigning ENV['PE_VER'] to @build.pe_version isn't functional
anymore. There should be no case where we pass ENV['PE_VER'] but doesn't
actually want this to get set as @build.pe_version. This commit also updates
(sorry, I know, atomic commits) the dependencies of pe:jenkins:uber_build to
include pl:fetch and pl:load_extras so that ENV['PE_VER'] is acknowledged and
its value set for @build.pe_version.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>