Change Bazel default android_manifest_merger to android.

The Firebase Android libraries contain lots of AARs with manifests that include
${applicationId}. As far as I can tell, tools/android/merge_manifests.py only
allows for substitution of ${packageName} and not arbitrary placeholder
substitution. The new aar_import rule exposes the AARs in <sdk>/extras which
include include the Firebase Android libraries.

RELNOTES: Default android_manifest_merger is now "android" which uses the official Android manifest merger. http://tools.android.com/tech-docs/new-build-system/user-guide/manifest-merger

--
MOS_MIGRATED_REVID=138109902
diff --git a/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java
index c31245d..d819df0 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java
@@ -364,7 +364,7 @@
     public boolean useAndroidResourceShrinking;
 
     @Option(name = "android_manifest_merger",
-        defaultValue = "legacy",
+        defaultValue = "android",
         category = "semantics",
         converter = AndroidManifestMergerConverter.class,
         help = "Selects the manifest merger to use for android_binary rules. Flag to help the"