Add Failure to get mirror list to known errors
Add Failure to get mirror list to known errors

Getting yum repository mirror lists can be rairly unreliable at times,
catch the error so it will be retried.
DEBUG: Could not retrieve mirrorlist http://mirrorlist.....

Change-Id: I084457df070c16f7cd714b1401be6bb6943030b8

openstack-packages/DLRN,openstack-packages/delorean,openstack-packages/delorean,openstack-packages/DLRN