Optionally support Docker 18.03 and 18.06

[MarcPow]

What this PR does / why we need it:

Allows users to optionally select Docker 18.03 or 18.06

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

#4029

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[MarcPow]

Ah - I may need to abandon this. Per @CecileRobertMichon in the tracking issue, there are some licensing restrictions that prevent me from making this change.

[jackfrancis]

Can't do this due to licensing issues. moby support is in-progress