Improve debugging

[ademariag]

When jsonnet fails to compile, the output does not easily allow to understand which target caused the jsonnet to fail.

Compiled working-target1 (1.86s)
Compiled working-target2 (1.86s)
Jsonnet error: failed to compile repository/components/cloudsql-proxy/main.jsonnet:
 RUNTIME ERROR: field does not exist: cloudsql
        repository/components/cloudsql-proxy/main.jsonnet:13:26-49       object <anonymous>

One possible solution is to write the target being compiled before attempting the compilation. Output could look like this

Compiling working-target1  (OK 1.86s)
Compiling working-target2  (OK 1.86s)
Compiling failing-target3
Jsonnet error: failed to compile repository/components/cloudsql-proxy/main.jsonnet:
 RUNTIME ERROR: field does not exist: cloudsql
        repository/components/cloudsql-proxy/main.jsonnet:13:26-49       object <anonymous>

[adrianchifor]

Should we close #43 in favour of this?

[ademariag]

Didn't realize it was there already. It's the same really. Feel free to close this and don't feel constraint by my sample output ;)

[gburiola]

The problem with writing the target before starting the compilation is that the app is multithreaded, so you'll see 4 (default number of threads) in flight compilations