Fedora compresses the kernel with zstd now, which isn't suppported in
grub (as of 2.04). Since we don't care about PV that much anymore,
simply skip the test there.
Network may be configured (by qubes-misc-post service in some cases)
after qrexec is started. Delay any test after VM is fully started (as
the user would do).
Adjust wait_for_session function, to re-use VM startup timeout, which
make it adjustable for slower machines (like nested virt on openQA).
