[VVP] Add new columns to traceability report

[VVP] Add new columns to traceability report

Added the following columns:
* Keyword - MUST, MUST NOT, etc.
* Validation Mode - contents of :validation_mode: from vnfrqts
* Is Testable - TRUE if requirement is testable based on keyword
                and validation mode, FALSE otherwise

Also fixed issue following issues:
* Traceability and mapping error reports were not going to the
  configured output directory if a custom value was provided
* Removed duplicate rows from traceability report
* Traceability report shows all Heat requirements

Change-Id: I339b42e9e662f1681b78d1a49bd7e71e87cae21a
Issue-ID: VVP-148
Signed-off-by: Lovett, Trevor <trevor.lovett@att.com>