Run mkfs as root

The mkfs command requires root permission to write the filesystem on
certain devices. This patch is adding the run_as_root=True flag for the
execute() in the mkfs() function in common/utils.py, and is also adding
the mkfs to the rootwrap filters.

Closes-Bug: #1271243
Change-Id: I44e21c287510f355907fa45cbcb14b7f8c493a96
Merge "Run mkfs as root"