**Apache Airflow version**: 2.0.1

**Environment**:

- **Cloud provider or hardware configuration**: AWS

**What happened**:
I have Airflow with Cloudwatch-based remote logging running. I also have `BashOperator` that does, for example, `rsync` with invalid parameters, for example `rsync -av test test`. The output of the `rsync` error is formatted and contains empty line. Once that empty line is logged to the Cloudwatch, i receive an error:
```
2021-04-06 19:29:22,318] /home/airflow/.local/lib/python3.6/site-packages/watchtower/__init__.py:154 WatchtowerWarning: Failed to deliver logs: Parameter validation failed:
Invalid length for parameter logEvents[5].message, value: 0, valid range: 1-inf
[2021-04-06 19:29:22,320] /home/airflow/.local/lib/python3.6/site-packages/watchtower/__init__.py:158 WatchtowerWarning: Failed to deliver logs: None
```

So basically empty lines can't be submitted to the Cloudwatch and as result the whole output of the process doesn't appear in logs.

**What you expected to happen**:

I expect to have an output of the bash command in logs. Empty lines can be skipped or replaced with something.

**How to reproduce it**:

For example: run `BashOperator` with `rsync` command that fails on Airflow with Cloudwatch-based remote logging. It could be any other command that produces empty line in the output.
setup.py
'aws_xray_sdk',
    'beautifulsoup4~=4.7.1',
    'black',
    'blinker',
    'bowler',
    'click>=7.1,<9',
    'coverage',
    'filelock',
    'flake8>=3.6.0',
    'flake8-colors',
    'flaky',
    'freezegun',
    'github3.py',
    'gitpython',
    'ipdb',
    'jira',
    'jsondiff',
    'mongomock',
    'moto~=2.2, >=2.2.12',
    'parameterized',
    'paramiko',
    'pipdeptree',
    'pre-commit',
    'pypsrp',
    'pygithub',
    'pysftp',
    'pytest~=6.0',
    'pytest-asyncio',
    'pytest-cov',
    'pytest-instafail',