DDP Logdir Multiple Runs Bug
🐛 Bug

Using accelerator="ddp" and running a pl Experiment mulitple times each time creating a new Trainer, the log version number is handled in a wrong way.
Instead of creating folder "version_2" after running "version_1" a folder with name "2" is created.
To fix this, after the training, os.environ.pop("PL_EXP_VERSION") has to be executed.
Please reproduce using the BoringModel and post here

https://colab.research.google.com/drive/1GFQ6doCWl_aTdBaBVOgTf1dTs_qZV0sg?usp=sharing
Expected behavior

Increase "version_1" to "version_2".