specs: update openuri stubs

Matches puppetlabs_spec_helper's way of doing this.
couchdblookup() now always returns 'undef' when $::vagrantbox is defined
specs: be more specific when testing Puppet::ParseError
add tests for default value feature (added in e97e40811)
add test for bugfix added in 473bff7cf
specs: rename value for the sake of clarity
add Rakefile
add doc to couchdblookup() function
also honor 3rd argument when running in a vagrant environment
specs: mv helper files to fixtures/ dir
couchdblookup(): emit warning when executed on a vagrant box
Merge pull request #11 from mfournier/vagrant+tests+doc

Vagrant+tests+doc