"docker run" and "docker create" are mostly identical, so we can copy
the same completion functions,
We could possibly create a utility for this (similar to `addFlags()` which
configures both commands with the flags they share). I considered combining
his with `addFlags()`, but that utility is also used in various tests, in
which we don't need this feature, so keeping that for a future exercise.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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