(maint) Fix mocha expectations crashing facter_spec

Running `bundle exec rspec spec/unit/util/virtual_spec.rb
spec/unit/facter_spec.rb` prior to this patch would crash rspec outright
while the test harness was still loading.  This was because
virtual_spec.rb had expectations set in a shared_examples block but
outside of a before or it block.  These then caused an expectation
failure when explicit calls to Facter[:foo] were used as the description
in two describe calls in facter_spec.

This patch clears up both those misuses of rspec, and also adds the
log_spec_order method from Puppet for future bisecting of spec order
issues in Facter...which hopefully we won't have to do. :)
(maint) Rakefile loads all the libraries it can.

The call to load ext/packaging/packaging.rake will fail unless the
packaging system has been bootstrapped.  Previously this failure would
prevent attempts to load other libraries (notably rspec), and a `be rake
spec` would return silently without executing any specs.

Requires each lib separately so that failure to load one does not
prevent others.
(maint) Update README with a little bit of spec info.
Merge pull request #475 from jpartlow/maint/stable/virtual_and_facter_spec_order_fix

Maint/stable/virtual and facter spec order fix