Manage of additional filesystem types over webgui

[n1ete]

as already mentioned it would be a sweet addition to danube to manage lofs mountpoints for local storagepools for zones!
Zones are awesome on danube/smartos no overhead and full isolation. I use them a lot to run some stateless services for internal and external purpose so i thought it could be nice to manage Mounpoints from danube ui!

To use them over the webinterface would add features that are already working in danube and is just not exposed via gui.
a further read about latest development on vmadm reveals that you can even add and remove delegated datasets after vm creation, without destroying them! thats great news i think.

so i suggest to add these new "add_filesystem" and "remove_filesystem" functionality for all three filesystem types zfs/lofs/disk into Danube. at the moment only "disk" file type is managble over Danube UI and these two new filesystem types would integrate probably very well.

example of a command to add a lofs Filesystem in vmadm looks like this:

"add_filesystems": [
      {
        "type": "lofs",
        "source": "/zones/mailstore",
        "target": "/local/mailstore"
      }
    ]

to remove the same:

"remove_filesystems": [
      {
        "type": "lofs",
        "source": "/zones/mailstore",
        "target": "/local/mailstore"
      }
    ]

maybe the mountpoint sources should be predefined somewhere on node settings (since they are local only availble) and should then be selectable in Machines view per VM. as a surplus goal it would be nice to make the options 'ro' 'nodevice' selectable.
addding a lofs mount source needs a "does source exist" check.
target folder for lofs gets created if it does not exist.

i dont know if i am able to draft a pr for this. maybe you can help and give me some guidance where to start and what to look for.

[YanChii]

Very nice analysis. I like the idea of reusing the add-disk call. I'll think about it. At first look it should not be that hard to add it at least into API.
I'll let you know.
Thank you.