JSCBC-642: Added support for controlling tested features.
JSCBC-642: Added support for controlling tested features.

Motivation
----------
Some newer server features such as collections are manually
enabled and not controlled based on any obvious environment
information.

Changes
-------
Added ability to specify a feature being enabled/disabled
for a specific test run using CNFEAT=+some_feature.

Change-Id: I03d0c88214ed7db2a5c41d90e920b3d82d48b927
Reviewed-on: http://review.couchbase.org/119872
Reviewed-by: David Kelly <d83cd2a93a916ce0b0d4c1349b44be044799feca@gmail.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

couchbase/couchnode,couchbase/couchnode,couchbase/couchnode,brett19/couchnode,brett19/couchnode,brett19/couchnode,couchbase/couchnode