Existing logger conflict with lr_finder
🐛 Bug
If you call specific logger function (ie. add_histogram on a tensorboard one). The tuner will fails because it overwrite it with a DummyLogger (https://github.com/PyTorchLightning/pytorch-lightning/blob/master/pytorch_lightning/tuner/lr_finder.py#L150).
I would expect to not have to check if the logger I initiated in my trainer is being overwritten or not.
Additionally, on a minor minor note. I wouldn't expect progress_bar_refresh_rate to be overwritten as it is here.
Please reproduce using the BoringModel and post here

Expected behavior
Have a smooth way to ignore it.
Environment
* CUDA:
	- GPU:
		- Tesla T4
	- available:         True
	- version:           10.1
* Packages:
	- numpy:             1.18.5
	- pyTorch_debug:     True
	- pyTorch_version:   1.7.0+cu101
	- pytorch-lightning: 0.10.0
	- tqdm:              4.41.1
* System:
	- OS:                Linux
	- architecture:
		- 64bit
		- 
	- processor:         x86_64
	- python:            3.6.9
	- version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020


PyTorch Version (e.g., 1.0): 1.0
OS (e.g., Linux): colab
How you installed PyTorch (conda, pip, source): pip

Additional context
I am putting this as a bug because it is a behavior that required me to check into the source code to figure out where this DummyLogger came from. If the solution is non-trivial, a resolution could just be some warnings in the doc.