(re)create ext4 filesystems on the DUT in master mode

DebianBug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=762534
From: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Date: Tue, 23 Sep 2014 08:52:07 +0200

Recent versions of e2fsprogs in debian will give a warning when trying
to create a filesystem on a parition containing one and wait for user
input, this isn't very helpful for usage in a lava slave where the test
partitions get reformatted every run.

To work around this pass -F to mkfs.ext* and -f to mkfs.btrfs (woo,
standards...) to force filesystem creation.

Change-Id: I54e223501f0cd49a61c9c9c2550106512a32aa57
Merge branch 'master' into staging