Give user option to use buckd at their own risk.

To kill running buckd process:
  $ buck kill

Change-Id: Ie773f8f943c6e13e4a16f38fa6b62a1f69356f9b
diff --git a/tools/build/onos-buck b/tools/build/onos-buck
index 2129490..de1fb8f 100755
--- a/tools/build/onos-buck
+++ b/tools/build/onos-buck
@@ -41,5 +41,9 @@
 
 BUCK=$ROOT_DIR/bin/buck
 
+if [ "${ONOS_NO_BUCKD:-1}" == "1" ]; then
+  export NO_BUCKD=1
+fi
+
 # Finally, run the Buck command...
-NO_BUCKD=1 $BUCK "$@"
+$BUCK "$@"