**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
kubernetes = [
    'cryptography>=2.0.0',
    'kubernetes>=3.0.0, <12.0.0',
]
kylin = ['kylinpy>=2.6']
ldap = [
    'ldap3>=2.5.1',
    'python-ldap',
]
leveldb = ['plyvel']
mongo = [
    'dnspython>=1.13.0,<3.0.0',
    'pymongo>=3.6.0',
]
mssql = [
    'pymssql~=2.1,>=2.1.5',
]
mysql = [
    'mysql-connector-python>=8.0.11, <9',
    'mysqlclient>=1.3.6,<3',
]
neo4j = ['neo4j>=4.2.1']
odbc = [
    'pyodbc',
]
oracle = [
    'cx_Oracle>=5.1.2',
]
pagerduty = [
    'pdpyras>=4.1.2,<5',