replace git execs with vcsrepo

Use vcsrepo to manage Git repos used for installing rbenv itself and
various plugins rather than using execs that fire during every Puppet
application.
add vcsrepo dependency to Modulefile
fixed various syntax and compile errors...
added puppetlabs_spec_helper to Gemfile
added puppetlabs_spec_helper/rake_tasks to Rakefile
added .fixtures.yml, puts vcsrepo into place for testing
updated tests for vcsrepo

Tests on git execs are now testing the vcsrepo declarations. The test
covering plugin updates has been removed since ensure => latest on
vcsrepo should cover that.

Also fixed some errors caught by testing... yay tests!
cosmetic updates to fixtures.yml
removed existing files under spec/fixtures/modules

Using puppetlabs_spec_helper and .fixtures.yml means these files can be
automatically installed at test time rather than manually.
removed rspec-puppet plumbing

puppetlabs_spec_helper manages paths under spec/fixtures and finding
spec files, so that logic can be removed from Rakefile and spec_helper
updates to Gemfile.lock

Some of the modules under Gemfile.lock were pretty old and spamming test
output with deprecation warnings. Updated to use latest modules for
testing.
Change dependency to what we currently support
Merge pull request #2 from hubspotdevops/vcsrepo_for_plugins

Vcsrepo for plugins