Add get_ntp_peers()

[mirceaulinic]

As discussed in #12, will reimplement get_ntp_peers() to return a list of NTP peers as configured on the device.

[mirceaulinic]

@dbarrosop, @ktbyers does show ntp assoc on IOS returns the complete addresses for remote peers? (Please try with IPv6 -- on JunOS and EOS the output is truncated).

[dbarrosop]

Can we do a dictionary instead? Right now it's going to be a bit sad because it's going to be a dictionary with no values:

{
'192.168.0.1': {}
'17.72.148.53': {}
'37.187.56.220': {}
'162.158.20.18': {}
}

The reason is that you can stil do d.get_ntp_peers.keys() to get the list but doing a dict of dicts will allow us to extend this method to add more data if needed. Like the key used for authentication, or other configuration parameters. What do you think?

[mirceaulinic]

Although for the moment I don't see an obvious need, it is possible to need more information around NTP peers. Moreover would not cost very much to transform it into a dictionary.

[mirceaulinic]

@dbarrosop I finished updating the drivers, everything should be fine now.

[mirceaulinic]

@dbarrosop all clear now :)