default to package installation of nodejs on smartos

Since SmartOS and Node have the same maintainer, it seems easier (and more reliable) to install from Joyent packages than to do so from source.  Can still override the attribute if we want, of course.

In our case, installing from source was failing because the target ../src directory wasn't present.  Package-based install works nicely tho.

@eanakashima @bixu