Make running the tests like in travis-ci easier (#92)

* Move testing logic from travis.yml to tests-ci.sh script

This way we can share this logic between travis CI and other systems
like for example a docker container.

* Move logic to create a testing environment to tests-environment.sh

As with the logic to execute the tests, this way we can share this logic
with other systems to tests linuxdeployqt.

* Install Qt also in tests-environment.sh

No reason to keep it separate from the rest as far as I know

* Wait until the X server is up and running

Otherwise we get into a racy situation.

* Add Dockerfile to create a testing container

This container tries to emulate the environment we have in travis-ci,
this way we can test whatever is failing on the CI locally.

Dockerfile

@@ -0,0 +1,16 @@
+# This container amins to offer a testing environment similar to the one we are
+# creating in travis-ci so we can easily reproduce issues detected on our CI
+# locally
+#
+# To use it, simply execute the container like this:
+# docker run --rm -ti --privileged -v /path/to/linuxdeployqt:/linuxdeployqt bash
+# and then execute tests/tests-ci.sh
+
+FROM ubuntu:trusty
+
+RUN apt-get update && apt-get -y install software-properties-common wget build-essential \
+    autoconf git fuse libgl1-mesa-dev psmisc
+
+COPY tests/tests-environment.sh /
+
+RUN /tests-environment.sh