Bash for recipes instead of Dash

[ReillyBrogan]

As discussed in Matrix we should use bash for the script part of boulder recipes instead of dash. We can still integrate a tool like shellcheck to get recipe analysis down the road.

[sunnyflunk]

This needs a bit of process. First we need to optimise bash and dash so we can get accurate numbers. Maybe we can get bash to be fairly fast.

Then we measure the performance difference of the change to start the discussion.