ext4_utils: canonicalize slashes in paths

Simplify handling of slashes between directories in paths by
forcing them to have leading and trailing slashes as appropriate
when passed in to make_ext4fs, and then keeping all directory
paths with a trailing slash.

As a side effect, using "/" as the mountpoint is now supported.

Change-Id: I73fe709c26003a20b0bdf6504db16cc9e39edf9b
2 files changed