Support FreeBSD 10

FreeBSD 10.0 has "pkgng" of the new default package manager.
`pkg_info` and such commands has been removed from this version.

I added FreeBSD10 of os type, and tests for "pkgng".
add freebsd10 to oses of Rakefile
Merge pull request #349 from serverspec/support-freebsd-10

Support FreeBSD 10