Travis: Force installing OpenJDK8 for Android SDK compatibility

Travis CI upgraded their Xenial VMs to default to openjdk11, which
is not working properly for sdkmanager, so we can no longer accept
licenses for the SDK.

They don't really seem to care about providing a good alternative
for us from the few threads I read, so let's just force openjdk8
back.

.travis.yml

@@ -71,6 +71,10 @@ matrix:
       env: PLATFORM=android TOOLS=no TARGET=release_debug CACHE_NAME=${PLATFORM}-clang EXTRA_ARGS="warnings=extra werror=yes"
       os: linux
       compiler: clang
+      addons:
+        apt:
+          packages:
+            - openjdk-8-jdk
 
     - name: macOS editor (debug, Clang)
       stage: build
@@ -116,14 +120,14 @@ before_install:
 install:
   - pip install --user scons;
   - if [ "$TRAVIS_OS_NAME" = "linux" ] && [ "$PLATFORM" = "android" ]; then
+      export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64;
+      export PATH=/usr/lib/jvm/java-8-openjdk-amd64/jre/bin:${PATH};
+      java -version;
       misc/travis/android-tools-linux.sh;
     fi
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then
       export PATH=${PATH}:/Users/travis/Library/Python/2.7/bin;
     fi
-  - if [ "$TRAVIS_OS_NAME" = "osx" ] && [ "$PLATFORM" = "android" ]; then
-      misc/travis/android-tools-osx.sh;
-    fi
 
 before_script:
   - if [ "$PLATFORM" = "android" ]; then

misc/travis/android-tools-linux.sh

@@ -70,9 +70,10 @@ if [ ! -d $ANDROID_NDK_DIR ]; then
   echo
 fi
 
-echo "Installing: Android Tools ..."
 mkdir -p ~/.android && echo "count=0" > ~/.android/repositories.cfg
+echo "Installing: Accepting Licenses ..."
 yes | $ANDROID_SDK_DIR/tools/bin/sdkmanager --licenses > /dev/null
+echo "Installing: Android Build and Platform Tools ..."
 yes | $ANDROID_SDK_DIR/tools/bin/sdkmanager 'tools' > /dev/null
 yes | $ANDROID_SDK_DIR/tools/bin/sdkmanager 'platform-tools' > /dev/null
 yes | $ANDROID_SDK_DIR/tools/bin/sdkmanager 'build-tools;28.0.3' > /dev/null