Installer: Added a retry loop to do_mount

In order to provide some failsafe for slow devices (USB CD/DVD are common culprit) not being up and available by the time the installer attempts to mount them, added a retry loop (1 minute, albeit arbitrary) to hopefully give ample time for all devices to come up when being mounted.

OXT-16 #comment Added a retry loop to do_mount
Merge branch 'master' of https://github.com/pearsonk/installer