Code review comment for ~raharper/curtin:feature/enable-storage-vmtest-on-centos

We've updated the centos images to have the required packages for offline install. Jenkins node didnt have access to the yum repos so the vmtests were failing for multipath and iscsi. With that resolved, I've re-run those tests and have positive results from here:

https://jenkins.ubuntu.com/server/job/curtin-vmtest-devel-debug/103/console

Ran 40 tests in 309.102s

OK (SKIP=12)
Fri, 21 Sep 2018 06:40:34 +0000: vmtest end [0] in 316s