Specify compression explicitly in the backup profile, not only when
requested with --compress or --compress-filter.
This will allow to disable compression with --no-compress option, as the
default if no compression is specified in the profile is to use gzip.
FixesQubesOS/qubes-issues#4803
QubesException class is used with meaningful messages and should be ok
to use it directly as error message. For other exceptions, still use
full traceback (most likely a bug somewhere, not user error).
FixesQubesOS/qubes-issues#3610
New qvm-backup tool can either use pre-existing backup profile
(--profile), or - when running in dom0 - can create new one based on
used options (--save-profile).
This commit add a tool itself, update its man page, and add tests for
it.
FixesQubesOS/qubes-issues#2931
