Move from template to file_line for Karaf features

Move from template to file_line for Karaf features

We were configuring the set of Karaf features to install at start (set
via featuresBoot) using a template. This template in particular
frequently exposed the major problem with templates - they override new
upstream content and need a manual update each time it changes. This
implementation uses file_line to do a sed-like replace on the
featuresBoot list, without impacting the rest of the file (the Karaf
feature repos via featuresRepositories most importantly, as it changed
every ODL version bump).

New rspec-puppet tests were added for the file_line step, and the
original file tests were updated. The Beaker tests haven't changed and
are still passing, which is desired/expected since we want the same
functional output from the two implementations.

Change-Id: I2e4fffc02989c7f790128e2b69f3c055bd32492c
Signed-off-by: Daniel Farrell <dfarrell@redhat.com>