Use java_home to determine jdk location.

Specifying the major version rather than hard coding
to a minor version.

(cherry-picked from commit 13b2e19ef240804908629ed2e54a98ec9dede337)

Change-Id: Ie2c08d35fcff2129b26c1dfa8a2e5cd7b19c4b49
diff --git a/envsetup.sh b/envsetup.sh
index f75bf88..60726d3 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -1401,7 +1401,7 @@
       else
         case `uname -s` in
             Darwin)
-                export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents/Home
+                export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)
                 ;;
             *)
                 export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64