At present, `auto_unmount` option is recorded at PV annotation of glusterfs PV.
Due to the preference given in MountOptionFromSpec() for annotation mount options
over sc supplied mount options(Ref PR# https://github.com/kubernetes/kubernetes/pull/66576),
the sc supplied mount options are not honoured in glusterfs plugin
eventhough the driver returns `true` for storage class mountoptions
support at probe.

This patch removes `auto_unmount` option from annotation of the pv spec.
Signed-off-by: Humble Chirammal <hchiramm@redhat.com>