Add stdout and stderr to debug output for shell_command

[n8henrie]

Description:

shell_command is much easier to debug if its stdout and stderr are captured and made available in the log. As implemented in this PR, they will only been shown when shell_command logging verbosity is set to debug, allowing users to use that information when needed, but should not clutter the logs by default.

Related issue (if applicable):

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.github.io#<home-assistant.github.io PR number goes here>

Example entry for configuration.yaml (if applicable):

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[syssi]

Please add some notice about the feature at the docs.

[n8henrie]

home-assistant/home-assistant.io#5376