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
(cherry picked from commit 6e08e477a9cb46b1d371c2c9812e5ce9f4cf69be)

Conflicts:
	etc/neutron/plugins/cisco/cisco_plugins.ini
	neutron/plugins/cisco/common/config.py

Change-Id: I95747f35bae5b7157391c1698c0fe84d2126aa10
Merge "Increase the default poll duration for Cisco n1kv" into stable/icehouse