Only installing node from source on Linux

On linux, installing with apt results in an old version, but installing
from source works.  On SmartOS, installing from source would require
epic munging of the nad install with yet another patch to update the smf
manifest to include a different `LD_LIBRARY_PATH`.  Ugh.  So instead of
doing that, we're ensuring the lastest version with the `package`
provider.  If used on a SmartOS machine with nad already working, this
should have no effect
Merge remote-tracking branch 'origin/master' into installing-node-differently-per-os
Using preferred syntax for checking platform
Not specifying the version

Because apparently it gets updated quickly enough that specifying it
might break things.  Leaving it unspecified, however, shouldn't cause
any problems.
Merge pull request #17 from modcloth-cookbooks/installing-node-differently-per-os

Only installing node from source on Linux