libvirtError in _update_libvirt_domain is no longer silently swallowed.
libvirtError in _update_libvirt_domain is no longer silently swallowed.

I had some issue with fstrim and the missing else had caused the code to continue and fail later with a non-descriptive error message. This commit makes the error message more descriptive and helpful.

woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin