split pip tests to run separately for Ubuntu/trusty and Debian/stretch

Trying to reuse the pip test run is now a lot more work than just
writing it cutstom for each target platform.

Ubuntu/trusty does not have androguard 3.1.x nor aapt >= 26.x, so
using trusty's aapt will always have errors scraping some names from
APKs.  This continues to use Google's binary.

`apt-get update` is now disabled by default by Travis, this adds it
back so that the latest files from the PPA are used.

Here's one example of an issue with pip on trusty:
https://github.com/requests/requests/issues/4006

    pip3 install --quiet -e /home/travis/build/fdroidtravis/fdroidserver
    Exception:
    Traceback (most recent call last):
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/pkg_resources.py", line 2482, in _dep_map
        return self.__dep_map
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/pkg_resources.py", line 2344, in __getattr__
        raise AttributeError(attr)
    AttributeError: _DistInfoDistribution__dep_map

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python3.4/site-packages/pip/basecommand.py", line 122, in main
        status = self.run(options, args)
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python3.4/site-packages/pip/commands/install.py", line 278, in run
        requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python3.4/site-packages/pip/req.py", line 1266, in prepare_files
        req_to_install.extras):
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/pkg_resources.py", line 2291, in requires
        dm = self._dep_map
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/pkg_resources.py", line 2484, in _dep_map
        self.__dep_map = self._compute_dependencies()
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/pkg_resources.py", line 2517, in _compute_dependencies
        common = frozenset(reqs_for_extra(None))
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/pkg_resources.py", line 2514, in reqs_for_extra
        if req.marker_fn(override={'extra':extra}):
      File "/home/travis/build/fdroidtravis/fdroidserver/env/lib/python-wheels/setuptools-3.3-py2.py3-none-any.whl/_markerlib/markers.py", line 113, in marker_fn
        return eval(compiled_marker, environment)
      File "<environment marker>", line 1, in <module>
    NameError: name 'platform_system' is not defined

.travis.yml

@@ -24,27 +24,18 @@ matrix:
 # is used on Windows Subsystem for Linux.
 addons:
   apt:
+    update: true
     sources:
       - sourceline: 'ppa:fdroid/fdroidserver'
     packages:
-    - bash
-    - dash
-    - pylint
-    - pep8
-    - python3-babel
-    - python3-dev
-    - python3-pip
-    - python3-ruamel.yaml
-    - python3-setuptools
-    - python3.4-venv
-    - libjpeg-dev
-    - zlib1g-dev
-    - fdroidserver
+      - python3-babel
+      - python3-setuptools
+      - fdroidserver
 
 android:
   components:
     - android-23  # required for `fdroid build` test
-    - build-tools-25.0.3  # required for `fdroid build` test
+    - build-tools-27.0.3  # required for `fdroid build` test
   licenses:
     - 'android-sdk-preview-.+'
     - 'android-sdk-license-.+'
@@ -101,15 +92,12 @@ install:
     fi
 
 # The OSX tests seem to run slower, they often timeout.  So only run
-# the test suite with the installed version of fdroid, instead of the
-# three rounds that ./complete-ci-tests does.
+# the test suite with the installed version of fdroid.
+#
+# Supporting pip on Ubuntu/trusty was too painful here, since it seems
+# that pip installs conflict with the Ubuntu packages.
 script:
-  - cd tests
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
-      ./run-tests;
-    else
-      ./complete-ci-tests;
-    fi
+  - ./tests/run-tests
 
 after_failure:
   - cd $TRAVIS_BUILD_DIR