Respect GRAVITY_STATE_DIR when activating venv

[nsoranzo]

So that something like:

export GRAVITY_STATE_DIR=/srv/galaxy/gravity
./run.sh

writes gravity state/log files to the right place.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. Start Galaxy as mentioned above
  2. Check that gravity writes to the correct directory

License

• I agree to license these contributions under Galaxy's current license.
• I agree to allow the Galaxy committers to license these and all my past contributions to the core galaxy codebase under the MIT license. If this condition is an issue, uncheck and just let us know why with an e-mail to galaxy-committers@lists.galaxyproject.org.

[mvdbeek]

I suppose #13692 is the side effect of this change

[nsoranzo]

run.sh doesn't leak GRAVITY_STATE_DIR into the environment, so I think it was manually set.

[jdavcs]

I suppose #13692 is the side effect of this change

Not this one, it's setting it in the venv's activate script: deactivating the venv won't unset it, so it persists.