update volume api fvt
update volume api fvt

fix bugs in fvt code and add detach test

Change-Id: I155eddd628a96e53cf7fe9af2a9e88e6e929b220

mfcloud/python-zvm-sdk,mfcloud/python-zvm-sdk,mfcloud/python-zvm-sdk,mfcloud/python-zvm-sdk