Add automatic file_contexts handle to make_ext4fs.

Normal make_ext4 use requires a -S option to
pass a correct file_contexts path for labeling.
This becomes impractical under certain conditions
when used on a target device.  For instance, with
the creation of ext4 containers for asec images.
This patch will create a proper sehandle only
if the -S option is not used and only when
run on a target device.

Change-Id: I9bdc8659aae7037ccebbf4464500b79b4b2f56af
3 files changed