Fail "gracefully" in VTS when a VINTF Manifest can't be parsed

Add a failure with a message telling the user to look into the logs to
find out why the Manifest failed to be parsed.

Test: Modify /vendor/etc/vintf/manifest.xml on-device to be invalid and
run 'atest vts_treble_vintf_vendor_test'
Bug: 382290456

Change-Id: I6daadcbea7ea380d2c676155ac819ed4141640fc