Increase the default poll duration for Cisco n1kv

Increase the poll duration for Cisco N1Kv, from 10s to 60s and also
clean up the /etc/neutron/plugins/cisco/cisco_plugins.ini file. The
current poll duration of 10s causes that VSM to unnecessarily taking
frequent CPU cycles, resulting in the failure of other tasks in scale
configurations.

Closes-Bug: 1357030

Change-Id: I95747f35bae5b7157391c1698c0fe84d2126aa10
Merge "Increase the default poll duration for Cisco n1kv"