suricatasc: Use better exception message, sort imports

suricatasc: Use better exception message, sort imports

Up until now, suricatasc gives a message as follows in case a command is
missing arguments:
```
>>> list-hostbit
Arguments to command 'list-hostbit' is missing
```

Fix this up and provide a better message:
```
>>> list-hostbit
Missing arguments: expected 1
>>> pcap-file-continuous
Missing arguments: expected at least 2
```