Fix empty hash console rendering bug

Previously, if a face action returned an empty hash Puppet would print
out an error something like the following:

    err: undefined method `+' for nil:NilClass
    err: Try 'puppet help stack build' for usage

The cause of the error was a method in network/formats.rb that did not
account for the possibilty of an empty hash. This commit resolves the
issue by adding logic to account for the empty hash scenario, rendering
an empty hash as an empty string.
Merge branch 'reidmv-fix/master/formats_render_empty_hash'

* reidmv-fix/master/formats_render_empty_hash:
  Fix empty hash console rendering bug

closes #1380