The purpose of this class is helping us to handle the nfs related ops using in our tests so we can set up the nfs support in the host just with the cfg files. It is just a very basic class for handle just one nfs(remote or export from localhost). As the remote and exported nfs is only different in the export step. I put them in the same class. The NFSBASE and NFS seems can not really represent the purpose of the classes.  And I want to add some code later in env_process.py for handling nfs needed in tests configured by the cfg files. Not include them in this one just because it will conflict with iscsi pullreq.