replace_file(), rename_file(), and remove_file() now have optional
'logger' and 'log_level' (defaulting to DEBUG) arguments.
replace_file() now has a required 'permissions' and an optional
'close_on_success' (defaulting to True) argument. Also, it doesn't
create any directories; and in case of an exception, the tempfile is
removed even when closing it raises another exception.
remove_file() now returns a value: True if the file was removed, or
False if it already didn't exist.
(fsync_path() is unchanged.)
!!! After cherry-picking for release4.0, consider a fixup !!!
!!! adding 'import qubes.utils' to storage/reflink there !!!
c988a2218b