Fix the code writing commands to the fail2ban socket to correctly encode
the command terminator string. The terminator string should be encoded as
a simple byte array, not using the pickle format. Using the pickle format
allowed the first command to succeed, but would "break" the socket in the
sense that all following commands would fail with an underflow exception.
Add support for sending a ping command to the fail2ban server over the
socket file. This includes encoding the command data using og-rek and
decoding the response using `gopickle`.