(maint) Includes missing spec_helper in three specs.

spec/spec_helper was missing from three of the specs. This showed up
because spec/unit/pops/containment_spec.rb just happened to come first
in the order of specs to be executed on our Solaris build, and began
causing failures because puppet/pops was being loaded prior to
spec_helper and puppet.  It was also causing rspec/mocha setup and
teardown failures, presumably because of rspec configuration being
called after this initial spec was loaded.

This commit ensures that each of these specs requires spec_helper first
so that spec and the puppet environment initialize properly regardless
of whether these specs run first or come later in the spec ordering.
Merge pull request #1727 from jpartlow/maint/added-missing-spec-helper

(maint) Includes missing spec_helper in three specs.