nmci.pexpect: fix _pexpect_complete()
If user does something like:
x = nmci.pexpect.pexpect_spawn()
...
x.close()
then _pexpect_complete()
would crash on executing .expect()
on
already closed process, which is unfotunate.
Also, do not rely on .status
being set,
use .isalive()
and .closed
instead.