Return mtu -1 and speed -1.0 if regex does not find the data in nxos_ssh

[ubaumann]

I have a Nexus with a display bug. This PR should make the NXOS driver a little more stable but I tottaly understand if you don't want to merge it.

If the regex search for MTU and speed fails, MTU -1 and speed -1.0 will be returned instead.

The cisco bug I am facing:

On some interfaces it does not show the MTU in the show interface

Ethernet1/2/3 is down (Link not connected)
  Hardware: 10/100/1000 Ethernet, address: 0cd9.9608.0d6f (bia 0cd9.9608.0d6f)
, BW 23 Kbit, DLY 10 usec

Correct would be:

Ethernet1/2/3 is down (Link not connected)
  Hardware: 10/100/1000 Ethernet, address: 0cd9.9608.0d6f (bia 0cd9.9608.0d6f)
  MTU 9612 bytes, BW 23 Kbit, DLY 10 usec

[mirceaulinic]

Code looks good. Would you be able to add a test case for this?

[ubaumann]

Of course. I copied the data from the normal test case and modiefierd it

[mirceaulinic]

Thanks @ubaumann !