libvirt-guests.sh: Declare and assign separately to avoid masking return values

libvirt-guests.sh: Declare and assign separately to avoid masking return values

In Bash, the following code does not do what you think it does:

  func() {
      local var=$(false)
      echo $?
  }

Here, '0' is echoed even though false is designed to exit with a
non-zero code. This is because in fact the last executed command
is 'local' not 'false' and thus '$?' contains zero as in "yeah,
the variable is successfully declared" [1]. In our libvirt-guest
shell script, there are a few places like this. Fix them.

1: bash_builtins(1)
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>