Test Qcow2 conversion

The qcow2 image is still on my server and should be moved to a shared LAVA
server.

Change-Id: Iec3096170bd1247183062135d1f74e4485550674
Test download of local image (file:// scheme)

Change-Id: Ie09b848d16305760f014516ce7c4300597c761c0
Remove ChecksumAction

This actions is empty as the download action is already computing checksums on
the fly.

Change-Id: I792bfc25e73679b49bd8c88422f1ce6c07da31ce
Add support for nfsroot

LAVA-1703 - tftp support for deploying to nfsroot.

Change-Id: Ifea98b0045624831465bcf707b300f33e7d652f5