android build: less verbose buildozer logs

.travis.yml

@@ -51,7 +51,11 @@ jobs:
         - sudo docker build --no-cache -t electrum-android-builder-img electrum/gui/kivy/tools
       script:
         - sudo chown -R 1000:1000 .
+        # Output something every minute or Travis kills the job
+        - while sleep 60; do echo "=====[ $SECONDS seconds still running ]====="; done &
         - sudo docker run -it -u 1000:1000 --rm --name electrum-android-builder-cont -v $PWD:/home/user/wspace/electrum --workdir /home/user/wspace/electrum electrum-android-builder-img ./contrib/make_apk
+        # kill background sleep loop
+        - kill %1
         - ls -la bin
         - if [ $(ls bin | grep -c Electrum-*) -eq 0 ]; then exit 1; fi
       after_success: true