qemu: Drop @cmdret argument from qemuSecurityCommandRun()

qemu: Drop @cmdret argument from qemuSecurityCommandRun()

Every single caller of qemuSecurityCommandRun() calls the
function as:

  if (qemuSecurityCommandRun(..., &cmdret) < 0)
      goto cleanup;

  if (cmdret < 0)
      goto cleanup;

(modulo @exitstatus shenanigans)

Well, there's no need for such complication. There isn't a single
caller (and probably will never be (TM)), that would need to
distinguish the reason for the failure. Therefore,
qemuSecurityCommandRun() can be made to pass the retval of
virCommandRun() called under the hood.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>