Log sqlalchemy exception message in migration.py
Log sqlalchemy exception message in migration.py

The current code in migration.py suppress underlying exception message.
If Nova sql db configuration (eg. user, or permission) is incorrect, or
the query result is not as expected, nova-manage command will display
a confusing message, which may not help user to address the problem.
Need to log the exception message and stack trace, in order to improve
servicability.

Change-Id: I742f25dd643a7886a5fd5f66eee899ae5b17b439

JioCloud/nova_test_latest,edulramirez/nova,cernops/nova,orbitfp7/nova,barnsnake351/nova,scripnichenko/nova,petrutlucian94/nova,jianghuaw/nova,JianyuWang/nova,mgagne/nova,NeCTAR-RC/nova,mandeepdhami/nova,joker946/nova,BeyondTheClouds/nova,rahulunair/nova,akash1808/nova_test_latest,Metaswitch/calico-nova,zaina/nova,zzicewind/nova,akash1808/nova,cernops/nova,Tehsmash/nova,jianghuaw/nova,openstack/nova,barnsnake351/nova,jeffrey4l/nova,apporc/nova,alaski/nova,cloudbase/nova,adelina-t/nova,whitepages/nova,cernops/nova,tealover/nova,blueboxgroup/nova,adelina-t/nova,alexandrucoman/vbox-nova-driver,scripnichenko/nova,dawnpower/nova,silenceli/nova,JioCloud/nova,takeshineshiro/nova,gooddata/openstack-nova,Stavitsky/nova,phenoxim/nova,klmitch/nova,tangfeixiong/nova,eonpatapon/nova,j-carpentier/nova,iuliat/nova,kimjaejoong/nova,whitepages/nova,rajalokan/nova,ted-gould/nova,bgxavier/nova,affo/nova,tealover/nova,dims/nova,thomasem/nova,yatinkumbhare/openstack-nova,klmitch/nova,BeyondTheClouds/nova,belmiromoreira/nova,vmturbo/nova,rajalokan/nova,varunarya10/nova_test_latest,mikalstill/nova,petrutlucian94/nova,tudorvio/nova,phenoxim/nova,mmnelemane/nova,BeyondTheClouds/nova,akash1808/nova,gooddata/openstack-nova,dims/nova,sebrandon1/nova,Tehsmash/nova,openstack/nova,zhimin711/nova,jeffrey4l/nova,jianghuaw/nova,rahulunair/nova,raildo/nova,fnordahl/nova,thomasem/nova,cloudbase/nova-virtualbox,devendermishrajio/nova,mmnelemane/nova,NeCTAR-RC/nova,apporc/nova,sebrandon1/nova,vmturbo/nova,Metaswitch/calico-nova,openstack/nova,CEG-FYP-OpenStack/scheduler,gooddata/openstack-nova,Juniper/nova,yatinkumbhare/openstack-nova,silenceli/nova,mahak/nova,bgxavier/nova,hanlind/nova,takeshineshiro/nova,Yusuke1987/openstack_template,joker946/nova,felixma/nova,tudorvio/nova,zzicewind/nova,Francis-Liu/animated-broccoli,nikesh-mahalka/nova,cloudbase/nova,isyippee/nova,j-carpentier/nova,TwinkleChawla/nova,gooddata/openstack-nova,alexandrucoman/vbox-nova-driver,Yusuke1987/openstack_template,orbitfp7/nova,Francis-Liu/animated-broccoli,shail2810/nova,JioCloud/nova,JianyuWang/nova,eonpatapon/nova,bigswitch/nova,devendermishrajio/nova_test_latest,rahulunair/nova,felixma/nova,TwinkleChawla/nova,yosshy/nova,yosshy/nova,mgagne/nova,klmitch/nova,cyx1231st/nova,double12gzh/nova,shail2810/nova,JioCloud/nova_test_latest,ted-gould/nova,akash1808/nova_test_latest,double12gzh/nova,mahak/nova,jianghuaw/nova,kimjaejoong/nova,edulramirez/nova,iuliat/nova,alvarolopez/nova,blueboxgroup/nova,Juniper/nova,mikalstill/nova,bigswitch/nova,rajalokan/nova,Juniper/nova,MountainWei/nova,CCI-MOC/nova,belmiromoreira/nova,mandeepdhami/nova,mahak/nova,CloudServer/nova,raildo/nova,CloudServer/nova,vmturbo/nova,CCI-MOC/nova,alvarolopez/nova,sebrandon1/nova,devendermishrajio/nova,LoHChina/nova,alaski/nova,vmturbo/nova,MountainWei/nova,Stavitsky/nova,hanlind/nova,fnordahl/nova,cyx1231st/nova,hanlind/nova,ruslanloman/nova,isyippee/nova,rajalokan/nova,affo/nova,nikesh-mahalka/nova,zaina/nova,ruslanloman/nova,cloudbase/nova,CEG-FYP-OpenStack/scheduler,dawnpower/nova,LoHChina/nova,projectcalico/calico-nova,varunarya10/nova_test_latest,klmitch/nova,Juniper/nova,tangfeixiong/nova,mikalstill/nova,cloudbase/nova-virtualbox,noironetworks/nova,noironetworks/nova,devendermishrajio/nova_test_latest,zhimin711/nova,watonyweng/nova,projectcalico/calico-nova,watonyweng/nova