qemu: capabilities: Unconditionally set QEMU_CAPS_BLOCKDEV/QEMU_CAPS_BLOCKDEV_HOSTDEV...

qemu: capabilities: Unconditionally set QEMU_CAPS_BLOCKDEV/QEMU_CAPS_BLOCKDEV_HOSTDEV_SCSI

The cleanup of the code to always assume support for QEMU_CAPS_BLOCKDEV
will not be simple, so for now we hardcode the support and the code will
be cleaned up gradually.

We also disallow users to clear the flags via the namespace property or
qemu.conf configuration.

The change to the PPC64 test data originates from the fact that the
capability dump is not from the release version but is lacking one of
the necessary flags to enable -blockdev.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>