To trigger a scan by coverity, do the following:

* Commit all changes on the master branch
* Change to the "coverity_scan" branch
* git merge master
* make a change such that you can do a commit
* Commit and then push

This should fire off a run of coverity scan.

Do not make source code changes on the coverity_scan branch and don't
merge the branch back into master since the .travis.yml file is
different between the branch and master.

Commits to coverity_scan branch will only trigger the coverity scan
and won't do the normal build and test.  Commits to master branch will
do the normal clang and gcc builds and run tests.