travis: allow failure of the kernel job. It sometimes times out when travis is on heavy load (which is a false positive).
travis: apply the same hack I used to work around broken exit status and kernel checking to cppcheck checking its own code (use -j2). Speeds up by around 3-4 minutes per affected job.
Merge pull request #270 from matthiaskrgr/travis_kernel

travis: allow failure of the kernel job. It sometimes times out when travis is on heavy load (which is a false positive).