Fix generation of per-recipe task repositories

* fixes errors is task repo snapshot creation
* updates the beakerd tests to use a non-empty task library
* additional logging output for task library metadata updates
* capture mail in beakerd tests

Bug: 880855
Change-Id: I45e5045b7058a5b7bca0c18c5eafd557eed52c79
Merge "Fix generation of per-recipe task repositories" into develop