mounttab: Solaris/vfstab support

[domcleal]

The parsedfile provider for mounttab supports both fstabs and vfstabs, but augeasproviders only supports fstab today. The Vfstab module/lens is upstream in Augeas but awaiting a release.

Once released, either the augeas provider could be updated to support both lenses (a little messy) or we separate it into a new provider, then confine it by OS.

[domcleal]

Added support based on the unreleased vfstab lens in 0.3.0. If you want to use it, load vfstab.aug into /usr/share/augeas/lenses (or your packaged dir). For development, I've added augeas as a submodule and loaded lenses from there.