Multiple NFS shares

[huguesalary]

Added the ability to setup multiple NFS Shares

By default (changeable with xhyve-experimental-nfs-share-root, see below) NFS shares are rooted at /xhyve-nfsshares to avoid the situation where a NFS Share /usr would be mounted at /usr

2 backward incompatible changes:

• renamed xhyve-experimental-nfs-share to xhyve-experimental-nfs-share-enable
• change xhyve-experimental-nfs-share from being a boolean to a string slice taking multiple path to be shared via NFS
• NFS Shares are now mounted under a default directory /xhyve-nfsshares (the old code was mounting everything under / causing, for example, /usr to be mounted at /usr)

Other change:

• add xhyve-experimental-nfs-share-root to allow specifying where in the guest the NFS Shares will be rooted at

Here's an example of how to use:

docker-machine -D create -d xhyve --xhyve-disk-size 40000 --xhyve-memory-size 4000 --xhyve-cpu-count 2 --xhyve-experimental-nfs-share-enable --xhyve-experimental-nfs-share /Users --xhyve-experimental-nfs-share /usr/ --xhyve-experimental-nfs-share-root /nfsharesfromhost test

This command will share the host folders /Users and /usr in the guest at /nfsharesfromhost/Users and /nfsharesfromhost/usr

[huguesalary]

The PR doesn't get updated with latest changes for some reason.

Sorry for the spam...