(QENG-969) Fix bug introduced with last patch.

Last patch addressed some PR comments regarding coding style and led to bug
which is now fixed.

Signed-off-by: Wayne <wayne@puppetlabs.com>
Revert "Revert "(QENG-431) expanded and improved role support in beaker""
(QENG-431) (cleanup) expanded and improved role support in beaker

- cleanup in response to review comments
(QENG-431) (cleanup + split out filtering) expanded and improved role support in beaker

- split out filtering from applying the block to hosts
- block_on now determines if we have a filter or not
- run_block_on accepts both a set of hosts and an optional filter
Merge pull request #381 from waynr/feature/qeng-969-add-modify-tk-config-dsl-method

(QENG-969) Fix bug introduced with last patch.
Merge pull request #362 from anodelman/revert-343-revert-237-role-repair

(QENG-431) expanded and improved role support in beaker
(QENG-845) Beaker junit xml: XML Parsing error

- need to strip out invalid characters from strings before printing to
  xml, these characters are still invalid even if wrapped in a cdata
  tag