Support of commandline options for ethereum clients

[winsvega]

A client need to support following command line arguments to work with retesteth

• --ipcpath /home/user/ (geth.ipc added by the client)
• --db-path /home/user/tempdir (datadir)
• --test (tells the client to work in test mode)

[winsvega]

this options are different on client implementations and it would be good to have a standart here.

[winsvega]

only needed for ipc socket when retesteth is starting the client with a system call
example config script that retesteth uses to start a client instance:

https://github.com/ethereum/tests/blob/develop/Retesteth/aleth/aleth.sh