Another stab at travis

.travis.yml

@@ -2,22 +2,37 @@ language: android
 jdk: oraclejdk8
 sudo: false
 
+cache:
+  directories:
+    - ${TRAVIS_BUILD_DIR}/gradle/caches/
+    - ${TRAVIS_BUILD_DIR}/gradle/wrapper/dists/
+
+env:
+  global:
+    - ANDROID_API_LEVEL=26
+    - EMULATOR_API_LEVEL=26
+    - ANDROID_BUILD_TOOLS_VERSION=26.0.0
+    - ANDROID_ABI=armeabi-v7a
+    - ANDROID_TAG=google_apis
+    - ADB_INSTALL_TIMEOUT=20 # minutes (2 minutes by default)
+
 android:
   components:
+    - tools
     - platform-tools
     - tools
-    - build-tools-26.0.0
-    - android-26
-    - sys-img-armeabi-v7a-android-26
+    - build-tools-$ANDROID_BUILD_TOOLS_VERSION
+    - android-$ANDROID_API_LEVEL
+    - android-$EMULATOR_API_LEVEL
+    - sys-img-armeabi-v7a-google_apis-$ANDROID_API_LEVEL
+    - sys-img-armeabi-v7a-google_apis-$EMULATOR_API_LEVEL
     - extra-android-m2repository
     - extra-android-support
     - extra-google-m2repository
 
 before_script:
-  # Create and start emulator
-  - echo no | android create avd --force -n test -t android-26 --abi armeabi-v7a
+  - echo no | android create avd --force -n test -t "android-"$EMULATOR_API_LEVEL --abi $ANDROID_ABI
   - emulator -avd test -no-skin -no-audio -no-window &
   - android-wait-for-emulator
-  - adb shell input keyevent 82 &
 
 script: travis_wait 60 ./gradlew clean connectedAndroidTest -PdisablePreDex --stacktrace