Fix bug 271

Moves ct_extra_params to the end of the generated ct_run command.
This allows users to pass commands to the underlying emulator
using -erl_args. The included rt test demonstrates that it is
possible to pass an addtional option to ct_run and -erl_args at
the same time. Finally, the test executes in regular and verbose
modes because rebar constructs the ct_run command differently in
verbose mode.