Compare string values, not if strings are the same object (apache#14942)

I found this when investigating why the delete_worker_pods_on_failure flag wasn't working. The feature has sufficient test coverage, but doesn't fail simply because the strings have the same id when running in the test suite, which is exactly what happens in practice.

flake8/pylint also don't seem to raise their respective failures unless one side it literally a literal string, even though typing is applied 🤷‍♂️.

I fixed 2 other occurrences I found while I was at it.

Fixes unbound variable on MacOS (apache#14877)

Without it I get:

```
$ ./breeze
./breeze: line 28: @: unbound variable
```

Apache Airflow 1.10.15

- Fix `airflow db upgrade` to upgrade db as intended (apache#13267)
- Moved boto3 limitation to snowflake (apache#13286)
- `KubernetesExecutor` should accept images from `executor_config` (apache#13074)
- Scheduler should acknowledge active runs properly (apache#13803)
- Bugfix: Unable to import Airflow plugins on Python 3.8 (apache#12859)
- Include `airflow/contrib/executors` in the dist package
- Pin Click version for Python 2.7 users
- Ensure all statsd timers use millisecond values. (apache#10633)
- [`kubernetes_generate_dag_yaml`] - Fix dag yaml generate function (apache#13816)
- Fix `airflow tasks clear` cli command wirh `--yes` (apache#14188)
- Fix permission error on non-POSIX filesystem (apache#13121) (apache#14383)
- Fixed deprecation message for "variables" command (apache#14457)
- BugFix: fix the `delete_dag` function of json_client (apache#14441)
- Fix merging of secrets and configmaps for `KubernetesExecutor` (apache#14090)
- Fix webserver exiting when gunicorn master crashes (apache#13470)
- Bump ini from 1.3.5 to 1.3.8 in `airflow/www_rbac`
- Bump datatables.net from 1.10.21 to 1.10.23 in `airflow/www_rbac`
- Webserver: Sanitize string passed to origin param (apache#14738)
- Make `rbac_app`'s `db.session` use the same timezone with `@provide_session` (apache#14025)

- Adds airflow as viable docker command in official image (apache#12878)
- `StreamLogWriter`: Provide (no-op) close method (apache#10885)
- Add 'airflow variables list' command for 1.10.x transition version (apache#14462)

- Update URL for Airflow docs (apache#13561)
- Clarifies version args for installing 1.10 in Docker (apache#12875)

Apache Airflow Constraints 1.10.15

Apache Airflow Elasticsearch Provider

Apache Airflow Upgrade Check 1.3.0

- Fix wrong warning about class that was not used in a dag file (apache#14700)
- Fill DagBag from `dag_folder` setting for upgrade rules (apache#14588)
- Bugfix: False positives for Custom Executors via Plugins check (apache#14680)
- Bugfix: Fix False alarm in import changes rule (apache#14493)
- Use `CustomSQLAInterface` instead of `SQLAInterface` (apache#14475)
- Fix comparing airflow version to work with older versions of packaging library (apache#14435)
- Fix Incorrect warning in upgrade check and error in reading file (apache#14344)
- Handle possible suffix in MySQL version + avoid hard-coding (apache#14274)

Prepare for releasing Elasticsearch Provider 1.0.3 (apache#14748)

apache#14686 fixes an issues with ES logging that should be released asap. Since we just released the providers it makes sense to release this separately.

Add elasticsearch to the fixes of backport providers (apache#14763)

We have a new elasticsearch fix and it should be added to the release
of backport providers. This change updates the documentation for the
elasticserch release.

Add elasticsearch to the fixes of backport providers (apache#14763)

We have a new elasticsearch fix and it should be added to the release
of backport providers. This change updates the documentation for the
elasticserch release.

Apache Airflow 1.10.15rc1