Close DB session in StatsSender.run
Close DB session in StatsSender.run

DB session.remove() is called in StatsSender.run loop.
Now it fails once after postgres restart and works fine in next iteration.

Change-Id: I7c31e37184139e950e400a8dba4bcd2e86b3c8ef
Closes-Bug: #1401521

huntxu/fuel-web,eayunstack/fuel-web,nebril/fuel-web,nebril/fuel-web,eayunstack/fuel-web,zhaochao/fuel-web,huntxu/fuel-web,zhaochao/fuel-web,huntxu/fuel-web,prmtl/fuel-web,huntxu/fuel-web,nebril/fuel-web,zhaochao/fuel-web,huntxu/fuel-web,eayunstack/fuel-web,stackforge/fuel-web,SmartInfrastructures/fuel-web-dev,zhaochao/fuel-web,stackforge/fuel-web,SmartInfrastructures/fuel-web-dev,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,SmartInfrastructures/fuel-web-dev,zhaochao/fuel-web,eayunstack/fuel-web,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,eayunstack/fuel-web,prmtl/fuel-web,prmtl/fuel-web,prmtl/fuel-web,stackforge/fuel-web,prmtl/fuel-web