Fix gitlab-ci (update android-sdk/ndk/p4a)
Some of the last prs of this project fails gitlab-ci tests due to a debian's missing dependencies (openjdk-7-jdk) in the current gitlab-ci docker image. This commit fixes the gitlab-ci tests. Upgrading the mentioned package was not enough to bypass the tests errors and some changes were made:
- Force to build packages with the master branch of p4a because with the stable branch of p4a, the gitlab tests leads into build errors, due to changes into the latest kivy
- Install/update the android's sdk/ndk (to bypass error mentioned above)
- Move android-sdk/ndk install from android_sdk_downloader.py to gitlab-ci.yml file to make things easier when upgrading gitlab-ci tests
Should be mentioned that the current buildozer version (at writing time) is not supporting android-sdk>=26 and this commit prepares the build-ci for when buildozer supports it.