autotest: Update DUT proper fw RO/RW labels after a firmware update

The labels of fw version have to be updated. If only updating RW,
clear and add a fwrw_version label. If updating both RO and RW, clear
and add both fwro_version and fwrw_version labels.

BUG=chromium:555709
TEST=Ran the following tests and checked the labels:
test_that --board $BOARD --args "value=$RO_BUILD" DUT_IP provision_FirmwareUpdate
test_that --board $BOARD --args "value=$RW_BUILD" DUT_IP provision_FirmwareUpdate.rw_only

Change-Id: Ibc705ec1c0c70403993ab7aebc8e2ce729b24483
Reviewed-on: https://chromium-review.googlesource.com/320605
Commit-Ready: Wai-Hong Tam <waihong@chromium.org>
Tested-by: Wai-Hong Tam <waihong@chromium.org>
Reviewed-by: Dan Shi <dshi@google.com>
diff --git a/server/cros/provision.py b/server/cros/provision.py
index 0435669..db5be08 100644
--- a/server/cros/provision.py
+++ b/server/cros/provision.py
@@ -34,9 +34,20 @@
     return CROS_VERSION_PREFIX + ':' + image
 
 
-def fw_version_to_label(image):
+def fwro_version_to_label(image):
     """
-    Returns the proper label name for a firmware build of |image|.
+    Returns the proper label name for a RO firmware build of |image|.
+
+    @param image: A string of the form 'lumpy-release/R28-3993.0.0'
+    @returns: A string that is the appropriate label name.
+
+    """
+    return FW_RO_VERSION_PREFIX + ':' + image
+
+
+def fwrw_version_to_label(image):
+    """
+    Returns the proper label name for a RW firmware build of |image|.
 
     @param image: A string of the form 'lumpy-release/R28-3993.0.0'
     @returns: A string that is the appropriate label name.