mount module: execute the mount only after path validation

This avoids a stale situation where name/path contains some impossible path,
but gets configured (faultly) in fstab, and the module only fails after that,
when creating that path.

I bumped into this situation by a misconfiguration where the path name was set to an empty string, while mounting an nfs share.

The module failed with `msg: Error making dir : [Errno 2] No such file or directory: ''` but left /etc/fstab with a broken configuration that made the host unbootable.