Log more info when mke2fs fails on a guest
Log more info when mke2fs fails on a guest

We have a device not found issue, but it's unclear if the device
doesn't exist at all, or it's in the wrong place. When we fail, dump
out the contents of /dev for further review.

Change-Id: I8b66b8acadc1d50a5ea7befd5ca6874c1dedcb4e

Tesora/tesora-tempest,cisco-openstack/tempest,masayukig/tempest,cisco-openstack/tempest,vedujoshi/tempest,masayukig/tempest,Tesora/tesora-tempest,vedujoshi/tempest,bigswitch/tempest,LIS/lis-tempest,bigswitch/tempest,sebrandon1/tempest,zsoltdudas/lis-tempest,Juniper/tempest,LIS/lis-tempest,sebrandon1/tempest,zsoltdudas/lis-tempest,openstack/tempest,Juniper/tempest,openstack/tempest