Fix incr file install symlink mode to normal mode

Fix rose.config_processors.file: in incremental mode, when
`mode=symlink` is removed from a target, the target should be recreated,
instead of being left to point to a symlink.
Merge pull request #846 from matthewrmshin/fix-rose-app-run-file-symlink-remove

Fix incr file install symlink mode to normal mode