Allow user to specificy local_dir value

Previously the --local option assumed the local dir to be DIST_DIR.
Since in the actual use case, the branch where the VNDK snapshot is
built is different from the branch where this VNDK snapshot is
uploaded to, allow the user to specify the local dir as a command
line parameter.

Test: python update.py --local=<path to local dir> 28 -vv
Bug: 78279738
Change-Id: I98a86296076994c951b98457ef47c384d4cc940c