CI for boto: fix errors; add coverage; add skip for uncatchable ResourceWarning
closes #23680 
closes #23754
- [x] fixture modified / tests pass
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

EDIT2: The warning has been identified as being caused by a vendored `requests` from `botocore<1.11`, which is solved by raising the minimum version to `1.11` for the only CI job (`travis-36`) that is testing `boto`. 

This would then simultaneously run into #23754 due to a moto bug (spulec/moto#1924 / spulec/moto#1941), but setting the environment variables `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` to any dummy value fixes the issue (taken from spulec/moto#1952).

I'm also adding the `boto` tests to the `travis-37` job, just to have some more coverage in general (and the `travis-37` is by far the fastest job right now).

~EDIT: The warning has been identified as being caused by a vendored `requests` from `botocore<1.11`. Unfortunately, it's not possible to (just) increase the minimum version, as `botocore>=1.11` currently runs into #23754 due to a moto bug (spulec/moto#1941), which would (once #24073 is merged) that these  would just be skipped silently. Thus, I'm adding a the boto tests to the `travis-37` build with `botocore>=1.11`, which will start working once #23754 is skipped, while still testing `boto` on the `travis-36` job by forcing `botocore<1.11`.~