Include last error cause in Databricks API when retry is exhausted

[amoghrajesh]

The hook was discarding the underlying cause (DNS failure, 503, connection timeout) when raising after tenacity exhausted retries. All failures produced the same string, making the error unclassifiable by a retry policy. Including the last exception gives enough signal to distinguish a permanent config error from a transient API blip.

Earlier:

ERROR - Attempt 1 API Request to Databricks failed with reason: <Future at 0xffff7b93cd90 state=finished raised ConnectionError> source=airflow.task.hooks.airflow.providers.databricks.hooks.databricks.DatabricksHook loc=databricks_base.py:1134
ERROR - Attempt 2 API Request to Databricks failed with reason: <Future at 0xffff7b72e020 state=finished raised ConnectionError> source=airflow.task.hooks.airflow.providers.databricks.hooks.databricks.DatabricksHook loc=databricks_base.py:1134
ERROR - Attempt 3 API Request to Databricks failed with reason: <Future at 0xffff7b13b8e0 state=finished raised ConnectionError> source=airflow.task.hooks.airflow.providers.databricks.hooks.databricks.DatabricksHook loc=databricks_base.py:1134
ERROR - Task failed with exception source=task loc=task_runner.py:1649
AirflowException: API requests to Databricks failed 3 times. Giving up.

Now:

ERROR - Attempt 1 API Request to Databricks failed with reason: <Future at 0xffff76357df0 state=finished raised ConnectionError> source=airflow.task.hooks.airflow.providers.databricks.hooks.databricks.DatabricksHook loc=databricks_base.py:1140
ERROR - Attempt 2 API Request to Databricks failed with reason: <Future at 0xffff70137cd0 state=finished raised ConnectionError> source=airflow.task.hooks.airflow.providers.databricks.hooks.databricks.DatabricksHook loc=databricks_base.py:1140
ERROR - Attempt 3 API Request to Databricks failed with reason: <Future at 0xffff76354dc0 state=finished raised ConnectionError> source=airflow.task.hooks.airflow.providers.databricks.hooks.databricks.DatabricksHook loc=databricks_base.py:1140
ERROR - Task failed with exception source=task loc=task_runner.py:1649
AirflowException: API requests to Databricks failed 3 times (last error: HTTPSConnectionPool(host='dbc-68473ce9-7672.cloud.databricks.con', port=443): Max retries exceeded with url: /api/2.2/jobs/run-now (Caused by NameResolutionError("HTTPSConnection(host='dbc-68473ce9-7672.cloud.databricks.con', port=443): Failed to resolve 'dbc-68473ce9-7672.cloud.databricks.con' ([Errno -2] Name or service not known)"))). Giving up.

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