ART: Fix buildbot-build.sh

Fix infinite loop for unrecognized options.

Test: art/tools/buildbot-build.sh --host
Test: art/tools/buildbot-build.sh --mode=host
Change-Id: I9f3b53021d83ddef2dca89b414065b9ea0bfafbf
diff --git a/tools/buildbot-build.sh b/tools/buildbot-build.sh
index 2d26b48..963efa4 100755
--- a/tools/buildbot-build.sh
+++ b/tools/buildbot-build.sh
@@ -52,6 +52,9 @@
     shift
   elif [[ "$1" == "" ]]; then
     break
+  else
+    echo "Unknown options $@"
+    exit 1
   fi
 done