**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
'gevent>=0.13',
    'greenlet>=0.4.9',
]
atlas = [
    'atlasclient>=0.1.2',
]
azure = [
    'azure-batch>=8.0.0',
    'azure-cosmos>=4.0.0,<5',
    'azure-datalake-store>=0.0.45',
    'azure-identity>=1.3.1',
    'azure-keyvault>=4.1.0',
    'azure-kusto-data>=0.0.43,<0.1',
    'azure-mgmt-containerinstance>=1.5.0,<2.0',
    'azure-mgmt-datafactory>=1.0.0,<2.0',
    'azure-mgmt-datalake-store>=0.5.0',
    'azure-mgmt-resource>=2.2.0',
    
    'azure-storage-blob>=12.7.0,<12.9.0',
    'azure-storage-common>=2.1.0',
    'azure-storage-file>=2.1.0',
]
cassandra = [
    'cassandra-driver>=3.13.0,<4',
]
celery = [
    'celery~=5.1,>=5.1.2',
    'flower~=1.0.0',
]
cgroups = [