Fix Volume.extend and Volume.update_readonly_flag methods

Correct VolumeManager method signature called from Volume.extend and
Volume.update_readonly_flag methods for v1 and v2 api's.

Change-Id: I2ffb49112d39ad96b91a4173526502a5201666c6
Closes-Bug: #1293423
Closes-Bug: #1294178
Merge "Fix Volume.extend and Volume.update_readonly_flag methods"