Add an explicit no-op option for minimal containers that do not have echo

[vizowl]

In order to support data only volumes using minimal images #514 I have added an option that allows a no-op command to be explicitly specified - currently it is assumed to be echo which isn't necessarily available on a minimal image.

I have added a test and updated the documentation.

I am concerned that this approach essentially exposes an internal feature ...

[vizowl]

I messed up the code signoff so I will create a new pull request with a rebased commit ...

[defunctzombie]

Was there a new PR for this? This issue still persists.

[vizowl]

I only closed this pull request because I messed up the commit signing - there was another pull request here #517 which generated a lot of discussion but no solution. I just stopped using minimal containers for data only volumes ...

[saulshanabrook]

@vizowl Could I open a new PR with your code and sign off of it? I would love to GTM.

[saulshanabrook]

If anyone else if having this problem, you can use the cogniteev/echo image instead of tianon/true which was created expressly to work around this bug.

[aanand]

@saulshanabrook A preferred solution would be the one proposed in #874 - use container renaming so we don't have to have intermediate containers at all.