Update subprocess handling to avoid hangs / blocking.

[bdmartin]

• Update subprocess handling to read both stdout and stderr (to avoid hangs based on blocked pipes).
• Add a unit test to cover that use case.
  • This test case would hang before the changes and now it does not.

[bdmartin]

@msiemens - Is this something that makes sense to take?

[msiemens]

Hey @bdmartin, sorry for the long delay. Seems like you work with bigger repositories than me 🙂 I've merged your PR and will publish a new release in just a minute!

[msiemens]

Released in v2.3.0 🙂