IOS-XR get_route_to fix pyIOSXR.exceptions.XMLCLIError for some versions

[chonty]

See #958

On some versions of IOS-XR, get_route_to fails because the XML path (not sure what else to call it) had an element renamed from IP_RIBRoute to IP_RIBRouteTableName.

This PR fixes issue #958 and maintains backwards-compatibility using option B from my comment in the same issue.

Global variable IP_RIBRoute is used to store the default name 'IP_RIBRoute' and if the RPC call fails, it will suppress the exception (something still pops up and I don't know how to stop it), change the value of var IP_RIBRoute to 'IP_RIBRouteTableName' and try the RPC call again. Doing it this way means that we only need to fail once within the lifetime of a Napalm instance.

>>> import napalm
>>> driver = napalm.get_network_driver("iosxr")
>>> d = driver(
...     hostname="10.10.10.9",
...     username="napalm",
...     password="napalm",
... )
>>> d.open()
>>> a = d.get_route_to("10.202.0.56/29")

Original call was: <?xml version="1.0" encoding="UTF-8"?><Request MajorVersion="1" MinorVersion="0"><Get><Operational><RIB><VRFTable><VRF><Naming><VRFName>default</VRFName></Naming><AFTable><AF><Naming><AFName>IPv4</AFName></Naming><SAFTable><SAF><Naming><SAFName>Unicast</SAFName></Naming><IP_RIBRouteTable><IP_RIBRoute><Naming><RouteTableName>default</RouteTableName></Naming><RouteTable><Route><Naming><Address>10.202.0.56</Address><PrefixLength>29</PrefixLength></Naming></Route></RouteTable></IP_RIBRoute></IP_RIBRouteTable></SAF></SAFTable></AF></AFTable></VRF></VRFTable></RIB></Operational></Get></Request>
>>> a
{'10.202.0.56/29': [{'current_active': True, 'last_active': False, 'age': 2460657, 'next_hop': '10.10.10.10', 'protocol': 'bgp', 'outgoing_interface': '', 'preference': 12, 'selected_next_hop': False, 'inactive_reason': '', 'routing_table': 'default', 'protocol_attributes': {}}]}
>>> a
{'10.202.0.56/29': [{'current_active': True, 'last_active': False, 'age': 2460657, 'next_hop': '10.10.10.10', 'protocol': 'bgp', 'outgoing_interface': '', 'preference': 12, 'selected_next_hop': False, 'inactive_reason': '', 'routing_table': 'default', 'protocol_attributes': {}}]}

In the above Python output, the Original call was:... will appear on the first get_route_to call if IP_RIBRoute doesn't work. I couldn't figure out how to silence it.

[coveralls]

Coverage remained the same at 0.0% when pulling 4b952dc on chonty:xr-get_route_to into 14749bd on napalm-automation:develop.

[mirceaulinic]

LGTM. Thanks @chonty!