fix #2788: do not resume vms after backup if they were paused before

fix #2788: do not resume vms after backup if they were paused before

by checking if the vm is paused at the beginning and skipping the
resume now we also skip the qga freeze/thaw (which cannot work if the
vm is paused)

moved the 'vm_is_paused' sub from the api to PVE/QemuServer.pm so it
is available everywhere we need it.

since a suspend backup would pause the vm anyway, we can skip that
step also

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by: Fabian Ebner <f.ebner@proxmox.com>