check_procs test fails if there is no user with uid 501

thats because check_procs verifys there is a user for a
given uid filter. So even we use sample data for this
test, we still need a real user.

Signed-off-by: Sven Nierlein <Sven.Nierlein@consol.de>
travis-ci: Adjust "branch_pattern"

Modify the "branch_pattern" for the Coverity add-on so that it also
matches "coverity/master" and "coverity/maint".
travis-ci: Don't use Clang

Currently, there doesn't seem to be a way to configure Travis CI to omit
the Clang build on the coverity/* branches.

See: https://github.com/travis-ci/travis-ci/issues/1975