allow command line override

Allow override for vabc_cow version if specified from the command line.
If OPTIONS.vabc_cow_version is already defined, then we don't want to
modify this value since it was defined by --vabc_compression_param=

Test: th
Change-Id: I57b8129faf5caf9de1dc8ad96e7570214a9f3313
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index c0ff5d2..0b90b66 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -912,12 +912,13 @@
     # and install time performance. All OTA's with
     # both the source build and target build with VIRTUAL_AB_COW_VERSION = 3
     # can support the new format. Otherwise, fallback on older versions
-    if not source_info.vabc_cow_version or not target_info.vabc_cow_version:
-      logger.info("Source or Target doesn't have VABC_COW_VERSION specified, default to version 2")
-      OPTIONS.vabc_cow_version = 2
-    elif source_info.vabc_cow_version != target_info.vabc_cow_version:
-      logger.info("Source and Target have different cow VABC_COW_VERSION specified, default to minimum version")
-      OPTIONS.vabc_cow_version = min(source_info.vabc_cow_version, target_info.vabc_cow_version)
+    if not OPTIONS.vabc_cow_version:
+      if not source_info.vabc_cow_version or not target_info.vabc_cow_version:
+        OPTIONS.vabc_cow_version = 2
+      elif source_info.vabc_cow_version != target_info.vabc_cow_version:
+        OPTIONS.vabc_cow_version = min(source_info.vabc_cow_version, target_info.vabc_cow_version)
+      if OPTIONS.vabc_cow_version:
+        logger.info("Source or Target doesn't have VABC_COW_VERSION specified, using version: " + OPTIONS.vabc_cow_version)
     # Virtual AB Compression was introduced in Androd S.
     # Later, we backported VABC to Android R. But verity support was not
     # backported, so if VABC is used and we are on Android R, disable