update CONTRIBUTING with information about beaker

beaker has replaced our rspec-system tests. These new tests are run
differently. Before messing with our Rakefile, a good start is to just
document it.
Merge pull request #533 from igalic/contributing-beaker

update CONTRIBUTING with information about beaker
Support environment variable control for CustomLog
Merge pull request #527 from chieping/add-access-log-option

Support environment variable control for CustomLog
Fix rspec-puppet deprecation warnings

This commit changes all the spec tests to use contain_class
instead of include_class which is deprecated.
Merge pull request #534 from blkperl/spec_dep_warns

Fix rspec-puppet deprecation warnings
rspec-puppet's .nodeset.yml is now deprecated
Merge pull request #537 from igalic/contributing-beaker

rspec-puppet's .nodeset.yml is now deprecated
Added support for mod_include
Merge pull request #543 from psyco01/include

Added support for mod_include
Merge remote-tracking branch 'upstream/master'