qemu_migration: Rearrange some checks in qemuMigrationSrcIsAllowed()
qemu_migration: Rearrange some checks in qemuMigrationSrcIsAllowed()

Firstly, the check for disk I/O error can be moved into 'if
(!offline)' section a few lines below.
Secondly, checks for vmstate and slirp should be moved under the
same section because they reflect live state of a domain. For
offline migration no QEMU is involved and thus these restrictions
are not valid.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

olafhering/libvirt,zippy2/libvirt,nertpinx/libvirt,crobinso/libvirt,olafhering/libvirt,jfehlig/libvirt,libvirt/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,zippy2/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,libvirt/libvirt,jardasgit/libvirt,zippy2/libvirt,jardasgit/libvirt,jardasgit/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,crobinso/libvirt,nertpinx/libvirt,jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,nertpinx/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,libvirt/libvirt,jardasgit/libvirt,jfehlig/libvirt