**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
'cgroupspy>=0.1.4',
]
cloudant = [
    'cloudant>=2.0',
]
dask = [
    'cloudpickle>=1.4.1, <1.5.0',
    'dask<2021.3.1;python_version<"3.7"',  
    'dask>=2.9.0, <2021.6.1;python_version>="3.7"',  
    'distributed>=2.11.1, <2.20',
]
databricks = [
    'requests>=2.26.0, <3',
]
datadog = [
    'datadog>=0.14.0',
]
deprecated_api = [
    'requests>=2.26.0',
]
doc = [
    'click>=7.1,<9',
    
    'sphinx>=2.1.2, <3.5.0',
    'sphinx-airflow-theme',
    'sphinx-argparse>=0.1.13',
    'sphinx-autoapi==1.0.0',
    'sphinx-copybutton',
    'sphinx-jinja~=1.1',
    'sphinx-rtd-theme>=0.1.6',