pydrake: Should ensure that torch>=1.5.0 does not create an issue, relax warning

[EricCousineau-TRI]

In #12073, the solution (#12108) was to print a warning that points to this issue:
pytorch/pytorch#3059 (comment)

That pytorch issue was closed in the following commit, which is part of torch>=1.5.0:
pytorch/pytorch@ddff4ef

However, if I now test in a virtualenv with torch==1.5.1, our warning still triggers:

(
set -eux

drake_base=drake-20200718-bionic.tar.gz
drake_file=~/Downloads/${drake_base}
if [[ ! -f ${drake_file} ]]; then
  wget https://drake-packages.csail.mit.edu/drake/nightly/${drake_base} -O ${drake_file}
fi

cd $(mktemp -d)

python3 -m virtualenv -p python3 . --system-site-packages
set +eux
source ./bin/activate
set -eux

tar -xzf ~/Downloads/drake-20200718-bionic.tar.gz --strip-components=1
pip install torch==1.5.1

python3 -c 'import torch; from pydrake.examples.acrobot import AcrobotPlant; AcrobotPlant()'
)

I'm bringing this up b/c I'm looking into #13571 and isort, and in Anzu, our import logic gets a little messy if we leave the condition that pydrake should be imported before pytorch. (Also, false positives here are annoying.)

[EricCousineau-TRI]

Old repro is here:
#12073 (comment)

[EricCousineau-TRI]

Updated repro: branch | commit (still for torch==1.0.0)
Command:

cd drake/tmp
./repro.sh

[EricCousineau-TRI]

Up to commit 9732ec0, found that torch=={1.0.0, 1.1.0, 1.2.0, 1.3.0} all failed the ./repro.sh recipe.
However, torch=={1.4.0, 1.5.1} did not fail it.

Will see if this pattern aligns with Sean's example w/ AcrobotPlant() - but only testing torch=={1.3.0, 1.4.0, 1.5.1}

EDIT: Yup, pattern aligned. Failed on 1.3.0, but not other versions. Makes sense why 1.5.1 works, but dunno why 1.4.0 works, but 🤷

EDIT 2: Huh... when looking at pytorchs source, I really dunno why 1.4.0 works.
This command doesn't show any significant diffs, so they must've changed how they packaged things:

cd pytorch
git diff v1.3.0 v1.4.0 -- torch/__init__.py

EDIT 3: Testing versions:

• 1.5.1: Commit 5236cb4, does not warn, does not segfault (good)
• 1.4.0: Commit f77f4b1, warns, but does not segfault
• 1.3.0: Commit 19c8194, warns, and segfaults