--network parameter of read_ledger doesn't work

Steps to Reproduce:
1. Setup the pool with 'sandbox' network in config and write some txns.
2. Run `sudo su - indy -c "read_ledger --type domain --network sandbox"`.
=> Read_ledger works fine, sandbox domain ledger is shown.
3. Run `sudo su - indy -c "read_ledger --type domain --count --network live"`.
=> Sandbox domain ledger is shown.
Expected: error should be shown.

4. Stop indy-node, rename `/var/lib/indy/sandbox` to `/var/lib/indy/live`.
5. Run `sudo su - indy -c "read_ledger --type domain --count --network live"`.
=> 

root@fef6dd9bf54e:/var/lib/indy# sudo su - indy -c "read_ledger --type domain --network live"
Traceback (most recent call last):
File "/usr/local/bin/read_ledger", line 161, in <module>
ledger_data_dir = get_ledger_dir(args.node_name, args.client_name, args.network)
File "/usr/local/bin/read_ledger", line 75, in get_ledger_dir
dirs = os.listdir(config_helper.ledger_data_dir)
FileNotFoundError: [Errno 2] No such file or directory: '/var/lib/indy/sandbox/data'
 

Actual Results:
Read_ledger works only with network specified in indy_config.py.

Expected Results:
It should work with network specified in --network parameter (ideally, value from indy_config.py should be used as default value of --network parameter if it is not specified), or --network parameter should be removed from script parameters.