(RE-2466) Remove legacy config, roll into EL mock config

Now that we have internal mirrors of el4, the mock config doesn't need
to substantially deviate from the current EL mock config. Conditionals
are added here to add the group definitions for el4 and to not define
the epel repo for el4, but it is otherwise identical.
(maint) Enable build-tools repo on all EL dists for PE

Previously the build-tools repo was only enabled on el 5 and 6. With the
addition of the legacy mock to the template, el4 is also required. And
el7 has a build-tools repo available as well. This commit updates that
logic to just check for el and add the repo if on el.
(RE-2466) Remove legacy mock defined types

Previous commits removed the need for a legacy mock in templates by
adding a few conditional stanzas. This commit makes a similar change to
the puppet code, removing the pe_legacy_mock and pe_legacy_mockset
defined types. It also updates the pe_mocks and pe_mockset to include
el4 mocks for PE.
(maint) Make chroot_setup_cmd consistent in pe el mock template