Remove session.flush() and session.query() monkey patching
Remove session.flush() and session.query() monkey patching

Use custom Session class to avoid monkey patching of SqlAlchemy
Session instance.

blueprint db-session-cleanup

Change-Id: I7d40c20e585782403556f3587141805c197bfa64

SauloAislan/ironic,Tehsmash/ironic,supermari0/ironic,naototty/vagrant-lxc-ironic,dims/ironic,rackerlabs/ironic,rdo-management/ironic,debayanray/ironic_backup,pshchelo/ironic,JioCloud/ironic,dims/ironic,citrix-openstack-build/ironic-lib,varunarya10/ironic,NaohiroTamura/ironic,naototty/vagrant-lxc-ironic,redhat-openstack/ironic,citrix-openstack-build/ironic,faizan-barmawer/ironic-lib,bacaldwell/ironic,froyobin/ironic,ionutbalutoiu/ironic,ramineni/myironic,Tan0/ironic,faizan-barmawer/openstack_ironic,NaohiroTamura/ironic,bacaldwell/ironic,naterh/ironic,openstack/ironic-lib,openstack/ironic,NaohiroTamura/ironic-lib,devananda/ironic,citrix-openstack-build/ironic,emonty/ironic,ionutbalutoiu/ironic,faizan-barmawer/elytics,pshchelo/ironic,openstack/ironic,SauloAislan/ironic,hpproliant/ironic