Replace vpp-gcc job with vpp-cov job per-patch

Replace vpp-gcc job with vpp-cov job per-patch

- the original gcc job was intended to ensure that gcc
  builds worked to generate test coverage reports.  The
  vpp-cov-verify job produces test coverage reports
  per patch and stores them in the S3 7-day docs
  retention bucket.

Change-Id: I28c7c323ea8d673cdee66b85189e20029e63336d
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>