Make a separate travis job for android

Since the download and install of the android sdk sometimes takes very
long time, build and deploy android in a separate travis job. The
environment variable ANDROID=true is only used to be able to distinguish
the two oraclejdk7 jobs in the travis build matrix.

.travis.yml

@@ -7,7 +7,10 @@ jdk:
 matrix:
   include:
   - jdk: oraclejdk7
-    script: mvn -q deploy -P android --settings .travis-settings.xml -Dno.gem.deploy=true -Dandroid.device=test
+    script: mvn -q deploy --settings .travis-settings.xml -Dno.gem.deploy=true
+  - jdk: oraclejdk7
+    env: ANDROID=true
+    script: mvn -q deploy -P android -pl android --settings .travis-settings.xml -Dno.gem.deploy=true -Dandroid.device=test
     before_install:
       # Install base Android SDK
       - sudo apt-get update -qq