Improves travis setup.

[bernhardreiter]

• Puts popd on a line of its own, otherwise its return value will
  override the exit code of the dpkg-buildpackage command, causing a
  successful build, even with it failed.

[ghost]

I noticed this too a few days ago.

We probably need to deactivate the build requirement check.

[ghost]

Changed the branch to maintenance (next upcoming version). The failing unit test is fixed there.

[bernhardreiter]

We probably need to deactivate the build requirement check.

I'm not sure what you mean here.

(If debian packages are to be build by the CI, of course success should be checked. )

[ghost]

Trusty (used by travis) has all build dependencies except for redis and termstyle. (See also #536)

So we can't fulfill all the requirements without adding my own repositories.

(If debian packages are to be build by the CI, of course success should be checked. )

But they are not distributed, so we only check for "syntactic" correctness with this build.

Will merge and push additional fixes tomorrow.

[ghost]

We can't run the debhelpers' tests because of travis-ci/travis-ci#2231 (see log https://travis-ci.org/wagner-certat/intelmq/jobs/332231121#L779 )