slurmint: made the script more robust to different system configurations

[d4l3k]

This updates the slurmint script to be more robust to environment changes since we switched to a new slurm cluster.

It removes the hardcoded /home/ubuntu and uses venv provided by miniconda so we don't need virtualenv installed on the host.

See https://www.internalfb.com/intern/wiki/PyTorch_R2P/Development/Slurm/ for more information

Test plan:

env SLURM_INSTANCE_MASTER=... scripts/slurmint.sh

[facebook-github-bot]

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[codecov]

Codecov Report

Merging #516 (fd9b1e2) into main (42e9b44) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #516   +/-   ##
=======================================
  Coverage   94.78%   94.78%           
=======================================
  Files          65       65           
  Lines        3932     3932           
=======================================
  Hits         3727     3727           
  Misses        205      205           

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