Disable InsecureRequestWarning if ssl_verify is false in nxos driver

[floatingstatic]

I see many examples where NAPALM users utilizing the nxos driver are doing something like this in their code to work around cert warnings that are displayed:

import urllib3
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

One example blog post

This is well and fine but I believe that the intent of the ssl_verify optional_arg for the nxos driver is that we should not verify the certificate in addition to hiding any InsecureRequestWarning warnings that are displayed. This change disables InsecureRequestWarning when ssl_verify is false or none which is the default for this driver.

An explicit example setting ssl_verify=False (implicit by default) with the current master branch:

>>> import napalm
>>> driver = napalm.get_network_driver("nxos")
>>> device = driver(hostname="10.10.0.60", username="admin", password="admin", optional_args={"ssl_verify": False})
>>> device.open()
/Users/jmillay/.venvs/napalm/lib/python3.8/site-packages/urllib3/connectionpool.py:1013: InsecureRequestWarning: Unverified HTTPS request is being made to host '10.10.0.60'. Adding certificate verification is strongly advised. See: https://urllib3.readthedocs.io/en/1.26.x/advanced-usage.html#ssl-warnings
  warnings.warn(

With my proposed changes:

>>> import napalm
>>> driver = napalm.get_network_driver('nxos')
>>> device = driver(hostname="10.10.0.60", username="admin", password="admin", optional_args={"ssl_verify": False})
>>> device.open()