Customize the NFS -mapall param in /etc/exports

[tonivdv]

Currently the /etc/exports file gets configured with:

-mapall=$(id -u):$(id -g)

However it seems for some (#14) this causes permissions issues and needs to be replace with some other values or be substituted with -maproot=0

The idea would be to allow to send the /etc/exports params through the docker-machine-nfs command:

E.g.

./docker-machine-nfs [machine] --nfs-exports="-maproot=0"

[arosenhagen]

:+1:

[ckortekaas]

+1