nfs-get: handle "nfs://" URLs with port number and quick optim

[cnotin]

rpc-scan generates "nfs://" URLs with the port number in it, ex:

# ./rpc-scan.py --nfs  10.0.0.1
rpc://10.0.0.1:111	Portmapper
nfs://10.0.0.1:2049/test/
[...]

Then if we use those URLs with nfs-get it fails because "o.netloc" = "10.0.0.1:2049" which isn't a valid host