rbd: use helper functions from csi-common for VolumeCapability checking

The internal/csi-common package offers helper functions like
`IsReaderOnly()` and `IsBlockMultiNode()`. These should be used instead
of checking the VolumeCapability that is passed in a request in
different places.

This also suggested that adding the "ro" mount option in
`NodeServer.mountVolumeToStagePath()` is not appropriate, as the
csi-common helper `ConstructMountOptions()` can take care of that
already too.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

internal/csi-common/nodeserver-default.go

@@ -93,6 +93,14 @@ func ConstructMountOptions(mountOptions []string, volCap *csi.VolumeCapability)
 		}
 	}
 
+	// add "ro" in case the capabilities indicate READER_ONLY
+	rOnly := "ro"
+	if IsReaderOnly([]*csi.VolumeCapability{volCap}) {
+		if !MountOptionContains(mountOptions, rOnly) {
+			mountOptions = append(mountOptions, rOnly)
+		}
+	}
+
 	return mountOptions
 }