Also test things with strict_variables.

strict_variables = true in puppet.conf is awesome, as it
stops you being able to typo variable names accidentally.

However, a lot of forge modules are not strict compliant.

Lets, by default test everything with strict variables true
as an option. I just _always_ set this, rather than multiply
the number of builds we run.
Merge pull request #25 from bobtfish/master

Also test things with strict_variables.