Feature/el5 7 support

[rdark]

Added support for EL5,6 + 7 - it already works out of the box without issue, but there are some OS defaults installed in limits.d that most users probably won't want deleted

• define some defaults that are installed by the pam package that we don't want to override (this can be disabled by setting ulimit::use_default_ulimits = false)
• add puppet-lint config
• fix the name of the file when ensuring => absent
• add support for ulimit load priorities

[arioch]

Excellent stuff. Thanks for contributing!