Don't use ModelBase.save() inside of transaction
Don't use ModelBase.save() inside of transaction

'with session.begin()' makes some operations in one transaction.
session.begin() returns a transaction instance, then does some operations,
and will commit or rollback automatically before leaving the block.
ModelBase.save() always submit a commit, and that is not expected.
When we get a persistent object from database, we just modify the
object inside of block 'with session.begin()' and sqlalchemy will
update it, don't need method session.add() or ModelBase.save().

Closes-Bug: #1224429
Change-Id: I4af58e98b2783d3945d92e57680d58e7ae356a67

apporc/cinder,NetApp/cinder,bswartz/cinder,abusse/cinder,alex8866/cinder,blueboxgroup/cinder,nikesh-mahalka/cinder,mahak/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,rakeshmi/cinder,saeki-masaki/cinder,Accelerite/cinder,abusse/cinder,leilihh/cinder,cloudbase/cinder,tlakshman26/cinder-https-changes,nexusriot/cinder,github-borat/cinder,duhzecca/cinder,takeshineshiro/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,tlakshman26/cinder-https-changes,duhzecca/cinder,JioCloud/cinder,Akrog/cinder,phenoxim/cinder,nikesh-mahalka/cinder,j-griffith/cinder,julianwang/cinder,winndows/cinder,potsmaster/cinder,openstack/cinder,nexusriot/cinder,Nexenta/cinder,cloudbase/cinder,phenoxim/cinder,tlakshman26/cinder-new-branch,apporc/cinder,julianwang/cinder,tlakshman26/cinder-new-branch,Nexenta/cinder,dims/cinder,NetApp/cinder,scottdangelo/RemoveVolumeMangerLocks,manojhirway/ExistingImagesOnNFS,scality/cinder,hguemar/cinder,ge0rgi/cinder,sasukeh/cinder,Hybrid-Cloud/cinder,Datera/cinder,scottdangelo/RemoveVolumeMangerLocks,rakeshmi/cinder,openstack/cinder,winndows/cinder,mahak/cinder,takeshineshiro/cinder,j-griffith/cinder,alex8866/cinder,Accelerite/cinder,blueboxgroup/cinder,CloudServer/cinder,sasukeh/cinder,scality/cinder,eharney/cinder,Paul-Ezell/cinder-1,Akrog/cinder,github-borat/cinder,redhat-openstack/cinder,eharney/cinder,JioCloud/cinder,redhat-openstack/cinder,Paul-Ezell/cinder-1,petrutlucian94/cinder,petrutlucian94/cinder,Datera/cinder,potsmaster/cinder,manojhirway/ExistingImagesOnNFS,CloudServer/cinder,leilihh/cinder,Hybrid-Cloud/cinder,dims/cinder,saeki-masaki/cinder,hguemar/cinder,bswartz/cinder