RFE: report failed constraints

[sschaefer]

Currently, sinan reports which applications have failed constraints (missing dependencies), but doesn't report what the failed constraints were. (Nit: the report could add a newline character after each application.) E.g., currently it reports bcmvc_web has a failed constraint, but it would be useful to also report that the missing dependency is cowboy.

I understand that constraint satisfaction is under development, but this might be a step in that direction: the constraint failure output could be the input to the constraint satisfaction component.

[ericbmerritt]

@sschaefer this is something that is currently in process. I will leave this open until it actually gets resolved.