[vcloud_director] fixes so that non configured gateway are supported

Currently the get_edge_gateway call bombs on non-configured edge gateways as they don't contain all the expected fields and configuration.

This pull request fixes that by checking before traversing the xml. There is a second requirement that fills in the missing parts, but I wanted to submit this as it stops the code breaking on some environments. 

I've tested it on 4 different environments that are in different states, but acknowledge that more automation around this logic is a future requirement, once we can manipulate edge gateway configuration



/cc @nosborn