on_fit_start not triggering (master)
🐛 Bug
on_fit_start is not being triggered on master as of f46318e
To Reproduce
Steps to reproduce the behavior:

Install master
Run template with on_fit_start added (included below)
(identical behavior for single gpu, ddp_spawn and ddp)

Code sample
"""
Runs a model on a single node across multiple gpus.
"""
import os
from argparse import ArgumentParser

from pl_examples.models.lightning_template import LightningTemplateModel
from pytorch_lightning import Trainer, seed_everything

seed_everything(234)

class custom_template(LightningTemplateModel):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
    
    def on_epoch_start(self):
        print("on_epoch_start")

    def on_fit_start(self):
        print("on_fit_start")

def main(args):
    """ Main training routine specific for this project. """
    # ------------------------
    # 1 INIT LIGHTNING MODEL
    # ------------------------
    model = custom_template(**vars(args))

    # ------------------------
    # 2 INIT TRAINER
    # ------------------------
    trainer = Trainer.from_argparse_args(args)

    # ------------------------
    # 3 START TRAINING
    # ------------------------
    trainer.fit(model)


def run_cli():
    # ------------------------
    # TRAINING ARGUMENTS
    # ------------------------
    # these are project-wide arguments
    root_dir = os.path.dirname(os.path.realpath(__file__))
    parent_parser = ArgumentParser(add_help=False)

    # each LightningModule defines arguments relevant to it
    parser = LightningTemplateModel.add_model_specific_args(parent_parser, root_dir)
    parser = Trainer.add_argparse_args(parser)
    parser.set_defaults(gpus=2, distributed_backend='ddp')
    args = parser.parse_args()

    # ---------------------
    # RUN TRAINING
    # ---------------------
    main(args)


if __name__ == '__main__':
    run_cli()

Expected behavior
"on_fit_start" should be printed along with "on_epoch_start" but only "on_epoch_start" is printed