Fix a few things for changed build system.

- Make a useful .gitignore file.
- Fix build.sh to make it work with some of the changes
I originally made to that script for the third robot.
diff --git a/.gitignore b/.gitignore
index 0d20b64..e74fec8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
+output
 *.pyc
diff --git a/aos/build/build.sh b/aos/build/build.sh
index c7a4bc4..656e72d 100755
--- a/aos/build/build.sh
+++ b/aos/build/build.sh
@@ -41,7 +41,7 @@
 {
   'target_defaults': {
     'configurations': {
-	  '${PLATFORM}': {}
+	  '${OUT_NAME}': {}
     }
   }
 }