machine_learning_phase undefined in start_tasks.py

[mhauru]

The machine_learning_phase variable is referenced a few times in start_tasks.py, but it's undefined:

augur/augur/tasks/start_tasks.py

Line 144 in a786ac5

if machine_learning_phase.__name__ in enabled_phase_names:

augur/augur/tasks/start_tasks.py

Line 223 in a786ac5

ml_enabled_phases.append(machine_learning_phase)

augur/augur/tasks/start_tasks.py

Line 260 in a786ac5

if machine_learning_phase.__name__ in enabled_phase_names:

Probably just missing an import.

[sgoggins]

@ABrain7710 : This goes to one of my questions. I found the same thing. Let's fix this when we can. @IsaacMilarky : If you have time to address that would also be great!