Convert tests to use plain rspec-puppet

Tests in the new style produces the following documentation output:

abs
  should not eq nil
  should run abs() and raise an Puppet::ParseError
  should run abs(-34) and return 34
  should run abs("-34") and return 34
  should run abs(34) and return 34
  should run abs("34") and return 34

1 files changed, 1 insertions, 0 deletions

diff --git a/Rakefile b/Rakefile
index 13ee3d9..e136b8e 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,4 +1,5 @@
 require 'rubygems'
+# keep for compatibility for now
 require 'puppetlabs_spec_helper/rake_tasks'
 require 'puppet-lint/tasks/puppet-lint'
 PuppetLint.configuration.send('disable_80chars')