Manila-CI: Fix tempest config option
Manila-CI: Fix tempest config option

The tempest config option, "storage_protocol" for glusterfs_native
driver CI needs to be "glusterfs" instead of "GLUSTERFS", as the
glusterfs_native driver reports its storage_protocol to be
"glusterfs" using update_share_stats share driver method.

Closes-Bug: #1498624
Change-Id: I1031cfaeab629b5aab316e611e9aae1833cf857b

stackforge/devstack-plugin-glusterfs,stackforge/devstack-plugin-glusterfs