1. Output of `losetup` command contains `\n` - strip it.
2. Provide read-only option - if device info hasn't propagated to qubesd
yet, it will not be set automatically.
FixesQubesOS/qubes-issues#3146
Very few calls at client side really needs VM class name. So, even in
non-blind mode use just QubesVM class, to avoid strange cases depending
on blind mode being enabled or not. Then, have VM class name in 'klass'
property. If known at object creation time, cache it, otherwise query
qubesd at first access.
Booting a VM from cdrom require attaching the device before VM startup,
which is possible only in persistent mode. But for qvm-start --cdrom
adding a cdrom only temporarily, use new update_persistence() function
to convert the assignment to temporary one.
FixesQubesOS/qubes-issues#3055
