R1:d1fd2975b062

Fail in a more comprehensible way when a WorkingCopy lease omits or mangles "repositories.map"

Summary: Ref T13676. When the required "repositories.map" attribute is omitted, `bin/drydock lease` currently fatals in an unhelpful way when trying to lease a working copy.

Test Plan:
Ran `bin/drydock lease --type working-copy` with no attributes, after following steps in T13676.

```
<Allocation Failed> One or more blueprints promised a new resource, but failed when allocating: [PhutilAggregateException] All…