don't require no_root_squash on NFS, only recommend

Ben Bodenmillerrequested to merge
bbodenmiller/gitlab-ce:patch-18 into master

What does this MR do?

I don't think no_root_squash is required anymore based on omnibus-gitlab!689 (merged) and https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/configuration.md#disable-storage-directories-management specifically:

Some types of mounts won't allow automatic creation of directories by root user (default user for initial setup), eg. NFS with root_squash enabled on the share. To work around this the omnibus-gitlab package will attempt to create these directories using the directory's owner user.

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