Use 'SHOW CREATE ALL TABLES' instead of cockroach dump

[adammohammed]

In CRDB v21.2 and newer cockroach dump is removed and the docs say to use SHOW CREATE ALL TABLES. This isn't quite a drop in replacement since it dumps some other non-sql information out.

This PR builds off of #41 and filters out the non-sql bits so that the generated tests still work.

Should fix #43 - but not sure if this is backwards compatible with previous CRDB releases.

[glerchundi]

LGTM, please rebase on top of master as it already includes the fix proposed in #41.

Thanks for the contribution, once rebased I will review ASAP.

[adammohammed]

@glerchundi Do you have time to take another pass at this?