[AIRFLOW-1740] Fix xcom creation and update via RBAC UI

[feluelle]

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Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-1740
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Description

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Fixes the xcom creation and update via the RBAC UI.
It fixes two issues:

1. sqlalchemy.exc.StatementError: (builtins.TypeError) memoryview: a bytes-like object is required, not 'str' [SQL: 'INSERT INTO xcom ("key", value, timestamp, execution_date, task_id, dag_id) VALUES (?, ?, ?, ?, ?, ?)'] [parameters: [{'value': 'value1', 'dag_id': 'example_bash_operator', 'key': 'key1', 'execution_date': datetime.datetime(2019, 7, 4, 16, 42, 23), 'task_id': 'run_me_0'}]]
2. sqlalchemy.exc.StatementError: (builtins.ValueError) naive datetime is disallowed [SQL: 'INSERT INTO xcom (key, value, timestamp, execution_date, task_id, dag_id) VALUES (%(key)s, %(value)s, %(timestamp)s, %(execution_date)s, %(task_id)s, %(dag_id)s) RETURNING xcom.id'] [parameters: [{'task_id': 'run_me_0', 'value': 'value1', 'dag_id': 'example_bash_operator', 'key': 'key1', 'execution_date': datetime.datetime(2019, 7, 4, 16, 30, 54)}]]

cc @ashb

Tests

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Documentation

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Code Quality

• Passes flake8