[bldr-build] Ensure functions that run in subshells use return.
[bldr-build] Ensure functions that run in subshells use return.

The `resolve_dep()` function was using `exit_with()`, but since it was
being called from a subshell and the return code was not being checked,
the program would continue after a bad depdency solve.

rsertelon/habitat,georgemarshall/habitat,georgemarshall/habitat,habitat-sh/habitat,habitat-sh/habitat,nathenharvey/habitat,habitat-sh/habitat,rsertelon/habitat,georgemarshall/habitat,georgemarshall/habitat,nathenharvey/habitat,georgemarshall/habitat,habitat-sh/habitat,nathenharvey/habitat,rsertelon/habitat,habitat-sh/habitat,nathenharvey/habitat,georgemarshall/habitat,habitat-sh/habitat,georgemarshall/habitat,nathenharvey/habitat,rsertelon/habitat,georgemarshall/habitat,habitat-sh/habitat,nathenharvey/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,habitat-sh/habitat