Feature dry run

Hello,

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This patch adds an option --dry-run to the run command.

In this mode changes to the database are prevented by a thin
layer around the the database object. Task action and teardown
execution is skipped.
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I did not test it thoroughly, its my first contribution :-). I did not add tests for the new code. Do you think this can be pulled ? Or what do you require for it being pulled ?


Thanks for your efforts,
Oliver
I guess this change wont be needed because teardown_list will always be empty on dry_run mode.