Fix build/deploy when installed without strongloop

If strong-arc is installed with `npm install -g strong-arc` and run as `strong-arc` (instead of `npm install -g strongloop` and `slc arc`), then there is no `slc build`. Rather than depending on strongloop, which would be a recursive dependency, depend on strong-build and invoke it using the same `require.resolve` trick that strongloop does for its commands.

/cc @sam-github