Define default mode and device_id_string in Mount
Define default mode and device_id_string in Mount

self.mode is not a valid class member in the Mount abstract class,
but used in map_dev(). Although all the subclasses define it so
there is no runtime bug, define it to avoid confusion and
better readability.

Do the same thing for device_id_string as precaution too.

Partially fix bug 1037183

Change-Id: Ica32db1ca17c6ed967f2c310b1d54adeb5f4247c

sridevikoushik31/nova,leilihh/novaha,phenoxim/nova,cloudbau/nova,tanglei528/nova,gooddata/openstack-nova,CiscoSystems/nova,maoy/zknova,watonyweng/nova,BeyondTheClouds/nova,LoHChina/nova,alaski/nova,houshengbo/nova_vmware_compute_driver,yrobla/nova,joker946/nova,kimjaejoong/nova,plumgrid/plumgrid-nova,cernops/nova,mmnelemane/nova,DirectXMan12/nova-hacking,adelina-t/nova,TwinkleChawla/nova,dstroppa/openstack-smartos-nova-grizzly,bgxavier/nova,bgxavier/nova,zzicewind/nova,j-carpentier/nova,iuliat/nova,JioCloud/nova,shahar-stratoscale/nova,houshengbo/nova_vmware_compute_driver,saleemjaveds/https-github.com-openstack-nova,mahak/nova,usc-isi/nova,mikalstill/nova,savi-dev/nova,TwinkleChawla/nova,cloudbau/nova,double12gzh/nova,ruslanloman/nova,hanlind/nova,tangfeixiong/nova,sridevikoushik31/openstack,ntt-sic/nova,sebrandon1/nova,Stavitsky/nova,joker946/nova,shahar-stratoscale/nova,takeshineshiro/nova,petrutlucian94/nova,noironetworks/nova,zaina/nova,jianghuaw/nova,yosshy/nova,viggates/nova,qwefi/nova,blueboxgroup/nova,DirectXMan12/nova-hacking,cernops/nova,sacharya/nova,JianyuWang/nova,SUSE-Cloud/nova,NewpTone/stacklab-nova,sridevikoushik31/nova,redhat-openstack/nova,TieWei/nova,tianweizhang/nova,dims/nova,Triv90/Nova,viggates/nova,yrobla/nova,devendermishrajio/nova_test_latest,maelnor/nova,BeyondTheClouds/nova,zaina/nova,akash1808/nova,savi-dev/nova,dawnpower/nova,mgagne/nova,mikalstill/nova,sridevikoushik31/openstack,luogangyi/bcec-nova,barnsnake351/nova,isyippee/nova,BeyondTheClouds/nova,ewindisch/nova,phenoxim/nova,shail2810/nova,tangfeixiong/nova,ntt-sic/nova,maoy/zknova,SUSE-Cloud/nova,cloudbase/nova,rahulunair/nova,savi-dev/nova,Juniper/nova,angdraug/nova,iuliat/nova,berrange/nova,jianghuaw/nova,mandeepdhami/nova,openstack/nova,rrader/nova-docker-plugin,petrutlucian94/nova_dev,rrader/nova-docker-plugin,barnsnake351/nova,alvarolopez/nova,OpenAcademy-OpenStack/nova-scheduler,isyippee/nova,alexandrucoman/vbox-nova-driver,vmturbo/nova,OpenAcademy-OpenStack/nova-scheduler,varunarya10/nova_test_latest,berrange/nova,apporc/nova,projectcalico/calico-nova,akash1808/nova_test_latest,NeCTAR-RC/nova,CCI-MOC/nova,luogangyi/bcec-nova,felixma/nova,saleemjaveds/https-github.com-openstack-nova,takeshineshiro/nova,tudorvio/nova,NewpTone/stacklab-nova,eonpatapon/nova,JioCloud/nova_test_latest,CEG-FYP-OpenStack/scheduler,maoy/zknova,CCI-MOC/nova,vmturbo/nova,dstroppa/openstack-smartos-nova-grizzly,CEG-FYP-OpenStack/scheduler,bigswitch/nova,aristanetworks/arista-ovs-nova,nikesh-mahalka/nova,rajalokan/nova,fajoy/nova,Yuriy-Leonov/nova,devoid/nova,cloudbase/nova,mahak/nova,Tehsmash/nova,JioCloud/nova_test_latest,virtualopensystems/nova,Yuriy-Leonov/nova,Stavitsky/nova,cloudbase/nova-virtualbox,qwefi/nova,fnordahl/nova,cyx1231st/nova,Tehsmash/nova,jeffrey4l/nova,blueboxgroup/nova,kimjaejoong/nova,fajoy/nova,klmitch/nova,edulramirez/nova,affo/nova,eharney/nova,ewindisch/nova,Francis-Liu/animated-broccoli,rickerc/nova_audit,sridevikoushik31/openstack,gspilio/nova,Juniper/nova,ruslanloman/nova,mahak/nova,rajalokan/nova,LoHChina/nova,MountainWei/nova,jianghuaw/nova,devendermishrajio/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,eayunstack/nova,tianweizhang/nova,usc-isi/nova,eayunstack/nova,zzicewind/nova,redhat-openstack/nova,noironetworks/nova,affo/nova,ted-gould/nova,edulramirez/nova,gooddata/openstack-nova,aristanetworks/arista-ovs-nova,rahulunair/nova,double12gzh/nova,citrix-openstack-build/nova,sebrandon1/nova,rahulunair/nova,akash1808/nova_test_latest,usc-isi/nova,badock/nova,maheshp/novatest,mandeepdhami/nova,thomasem/nova,cernops/nova,dims/nova,whitepages/nova,raildo/nova,openstack/nova,rajalokan/nova,cloudbase/nova-virtualbox,nikesh-mahalka/nova,paulmathews/nova,angdraug/nova,shail2810/nova,alvarolopez/nova,sridevikoushik31/nova,scripnichenko/nova,jianghuaw/nova,dstroppa/openstack-smartos-nova-grizzly,petrutlucian94/nova,tanglei528/nova,houshengbo/nova_vmware_compute_driver,JioCloud/nova,Yusuke1987/openstack_template,scripnichenko/nova,leilihh/novaha,mikalstill/nova,varunarya10/nova_test_latest,ted-gould/nova,j-carpentier/nova,plumgrid/plumgrid-nova,klmitch/nova,mgagne/nova,apporc/nova,Juniper/nova,sacharya/nova,vladikr/nova_drafts,alaski/nova,gooddata/openstack-nova,imsplitbit/nova,leilihh/nova,silenceli/nova,hanlind/nova,CloudServer/nova,NeCTAR-RC/nova,vmturbo/nova,shootstar/novatest,tealover/nova,cloudbase/nova,devendermishrajio/nova,raildo/nova,orbitfp7/nova,jeffrey4l/nova,maheshp/novatest,virtualopensystems/nova,watonyweng/nova,spring-week-topos/nova-week,orbitfp7/nova,akash1808/nova,belmiromoreira/nova,yatinkumbhare/openstack-nova,bigswitch/nova,yatinkumbhare/openstack-nova,badock/nova,alexandrucoman/vbox-nova-driver,rickerc/nova_audit,tealover/nova,sebrandon1/nova,adelina-t/nova,devoid/nova,devendermishrajio/nova_test_latest,maelnor/nova,belmiromoreira/nova,whitepages/nova,Juniper/nova,shootstar/novatest,Metaswitch/calico-nova,TieWei/nova,paulmathews/nova,eharney/nova,dawnpower/nova,klmitch/nova,fajoy/nova,sridevikoushik31/nova,NewpTone/stacklab-nova,yrobla/nova,zhimin711/nova,CloudServer/nova,aristanetworks/arista-ovs-nova,petrutlucian94/nova_dev,thomasem/nova,Triv90/Nova,yosshy/nova,CiscoSystems/nova,Triv90/Nova,Francis-Liu/animated-broccoli,mmnelemane/nova,zhimin711/nova,openstack/nova,gspilio/nova,felixma/nova,cyx1231st/nova,vmturbo/nova,Yusuke1987/openstack_template,MountainWei/nova,projectcalico/calico-nova,imsplitbit/nova,spring-week-topos/nova-week,silenceli/nova,klmitch/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,rajalokan/nova,gooddata/openstack-nova,hanlind/nova,fnordahl/nova,vladikr/nova_drafts,eonpatapon/nova,tudorvio/nova,DirectXMan12/nova-hacking,Metaswitch/calico-nova,leilihh/nova,bclau/nova,paulmathews/nova,maheshp/novatest,bclau/nova,JianyuWang/nova,citrix-openstack-build/nova,gspilio/nova