Enable '-t X' option in server mode

[TheRealDJ]

I would like the server side to dictate the maximum duration for a test. Maybe also add a '--force-duration X' to override a client's requested test duration also.

Ex 1: Server called with '-t 30' and client called with '-t 30' runs 30s test
Ex 2: Server called with '-t 30' and client called with '-t 15' runs 15s test
Ex 3: Server called with '-t 15' and client called with '-t 30' runs 15s test
Ex 4: Server called with '--force-duration 30' and client called with '-t 15' runs 30s test