No valid ethereum provider error when docker has not internet connectivity

[ghost]

Catch this error:

➜  ~ bash xud.sh
1) Simnet
2) Testnet
3) Mainnet
Please choose the network: 3
Pulling image exchangeunion/utils:20.08.29
🚀 Launching mainnet environment
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/launcher-1.0.0-py3.8.egg/launcher/__init__.py", line 260, in launch
    env = XudEnv(config, shell)
  File "/usr/local/lib/python3.8/site-packages/launcher-1.0.0-py3.8.egg/launcher/__init__.py", line 122, in __init__
    self.node_manager = NodeManager(config, shell)
  File "/usr/local/lib/python3.8/site-packages/launcher-1.0.0-py3.8.egg/launcher/node/__init__.py", line 121, in __init__
    self.nodes = {name: globals()[name.capitalize()](name, ctx) for name in self.config.nodes}
  File "/usr/local/lib/python3.8/site-packages/launcher-1.0.0-py3.8.egg/launcher/node/__init__.py", line 121, in <dictcomp>
    self.nodes = {name: globals()[name.capitalize()](name, ctx) for name in self.config.nodes}
  File "/usr/local/lib/python3.8/site-packages/launcher-1.0.0-py3.8.egg/launcher/node/geth.py", line 43, in __init__
    raise RuntimeError("No valid ethereum provider")
RuntimeError: No valid ethereum provider

...and display a nicer error message.