[pdal] First stab at Coverity Scan

[Mateusz Loskot]

Hi,

I've joined Andrew's efforst and I'm trying to configure Coverity Scan for PDAL.
I have configured it for several projects, including libLAS and
it generally is not a great deal of work.

However, with PDAL I'm hitting a wall.

I created new branch in PDAL/PDAL repo:

https://github.com/PDAL/PDAL/tree/coverity_scan

(Initially, I worked in mloskot/PDAL and I thought my problems
might be due missing some secret configs on GitHub/Travis CI.)

The build is failing with the error:

docker: command not found

https://travis-ci.org/PDAL/PDAL/jobs/180215967

In .travis.yml, I haven't changed anything regarding docker.
I only re-configured the build matrix a bit adding 3rd build for the Coverity.

I'm puzzled:
Why Travis CI properly sets up the docker service for the builds of master,
while it fails to do it for build based on coverity_scan branch?

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net