SDK support improvements.

Move figuring out the path to aidl/aapt/dx/llvm-rs-cc from IAndroidTarget
to SdkParser (in preparation of the build-tools).

Also change android.target to android.compileSdkVersion to make it
less confusing with regards to min/targetSdkVersion and also change it
to take either an int or a string.

Change-Id: I8642cb84f67cf75b49abe905b2a65f4d26668e98
diff --git a/tests/flavorlibWithFailedTests/app/build.gradle b/tests/flavorlibWithFailedTests/app/build.gradle
index dcaac3c..485c953 100644
--- a/tests/flavorlibWithFailedTests/app/build.gradle
+++ b/tests/flavorlibWithFailedTests/app/build.gradle
@@ -1,7 +1,7 @@
 apply plugin: 'android'
 
 android {
-    target = "android-15"
+    compileSdkVersion 15
 
     productFlavors {
         flavor1 {