Allow for specifying nfs mount options

Fixes bug 1113042

Adds a new config option:
    nfs_mount_options=None (Default)

When not None, anything set here will be passed as -o <options> to
the mount command. The default behavior is to do exactly as we are
doing today and relying on the OS/kernel defaults.

Change-Id: I6bd27f9d0e8848a9ba98318ba7288e43ee6b4cb9
Flags: DocImpact
Merge "Allow for specifying nfs mount options"