Committing a lock file using markFileChanged() required the input to
be writable by the caller in the local filesystem (using the path
returned by getSourcePath()). putFile() abstracts over this.
(cherry picked from commit 95d657c8b3ae4282e24628ba7426edb90c8f3942)
Change-Id: Ie081c5d9eb4e923b229191c5e23ece85145557ff