Use string.ascii_letters to be python 3 compatible
Use string.ascii_letters to be python 3 compatible

Use string.ascii_letters instead of string.letter. The only consequence
is to loose the locale-specific behavior but it seems not to be a bad
thing for generating a secret key.

Change-Id: Id985d798042eaa7541692d137027233537ed3bb4
Closes-Bug: #1360861

Mirantis/mos-horizon,newrocknj/horizon,yeming233/horizon,icloudrnd/automation_tools,BiznetGIO/horizon,takeshineshiro/horizon,Tesora/tesora-horizon,redhat-cip/horizon,BiznetGIO/horizon,promptworks/horizon,zouyapeng/horizon,Metaswitch/horizon,Daniex/horizon,endorphinl/horizon-fork,tqtran7/horizon,tsufiev/horizon,Dark-Hacker/horizon,tsufiev/horizon,Hodorable/0602,damien-dg/horizon,mrunge/horizon,maestro-hybrid-cloud/horizon,ChameleonCloud/horizon,redhat-openstack/horizon,NeCTAR-RC/horizon,Tesora/tesora-horizon,VaneCloud/horizon,xinwu/horizon,NCI-Cloud/horizon,VaneCloud/horizon,NCI-Cloud/horizon,dan1/horizon-x509,maestro-hybrid-cloud/horizon,nvoron23/avos,watonyweng/horizon,Daniex/horizon,redhat-openstack/horizon,henaras/horizon,vladryk/horizon,Mirantis/mos-horizon,nvoron23/avos,henaras/horizon,bac/horizon,FNST-OpenStack/horizon,icloudrnd/automation_tools,CiscoSystems/horizon,liyitest/rr,sandvine/horizon,newrocknj/horizon,j4/horizon,noironetworks/horizon,philoniare/horizon,Hodorable/0602,gerrive/horizon,eayunstack/horizon,anthonydillon/horizon,redhat-openstack/horizon,philoniare/horizon,froyobin/horizon,promptworks/horizon,mdavid/horizon,wangxiangyu/horizon,dan1/horizon-x509,dan1/horizon-x509,promptworks/horizon,coreycb/horizon,mdavid/horizon,wolverineav/horizon,mrunge/horizon_lib,coreycb/horizon,saydulk/horizon,mrunge/horizon_lib,orbitfp7/horizon,tqtran7/horizon,ChameleonCloud/horizon,yjxtogo/horizon,flochaz/horizon,newrocknj/horizon,henaras/horizon,kfox1111/horizon,zouyapeng/horizon,xinwu/horizon,mdavid/horizon,BiznetGIO/horizon,orbitfp7/horizon,Dark-Hacker/horizon,yjxtogo/horizon,dan1/horizon-proto,mandeepdhami/horizon,sandvine/horizon,Tesora/tesora-horizon,django-leonardo/horizon,redhat-cip/horizon,liyitest/rr,ging/horizon,CiscoSystems/avos,doug-fish/horizon,Hodorable/0602,NeCTAR-RC/horizon,mrunge/openstack_horizon,davidcusatis/horizon,endorphinl/horizon,philoniare/horizon,newrocknj/horizon,bac/horizon,tellesnobrega/horizon,yeming233/horizon,openstack/horizon,redhat-cip/horizon,sandvine/horizon,noironetworks/horizon,nvoron23/avos,orbitfp7/horizon,coreycb/horizon,xme1226/horizon,endorphinl/horizon-fork,tellesnobrega/horizon,openstack/horizon,CiscoSystems/horizon,django-leonardo/horizon,CiscoSystems/avos,nvoron23/avos,karthik-suresh/horizon,luhanhan/horizon,j4/horizon,maestro-hybrid-cloud/horizon,philoniare/horizon,henaras/horizon,CiscoSystems/avos,Tesora/tesora-horizon,flochaz/horizon,vladryk/horizon,doug-fish/horizon,redhat-openstack/horizon,Dark-Hacker/horizon,yjxtogo/horizon,xme1226/horizon,dan1/horizon-proto,takeshineshiro/horizon,Daniex/horizon,Mirantis/mos-horizon,anthonydillon/horizon,yeming233/horizon,BiznetGIO/horizon,mrunge/horizon,promptworks/horizon,wangxiangyu/horizon,blueboxgroup/horizon,CiscoSystems/horizon,froyobin/horizon,takeshineshiro/horizon,dan1/horizon-proto,agileblaze/OpenStackTwoFactorAuthentication,zouyapeng/horizon,RudoCris/horizon,xinwu/horizon,luhanhan/horizon,pranavtendolkr/horizon,yjxtogo/horizon,wangxiangyu/horizon,blueboxgroup/horizon,Metaswitch/horizon,tqtran7/horizon,dan1/horizon-proto,saydulk/horizon,wolverineav/horizon,watonyweng/horizon,Metaswitch/horizon,sandvine/horizon,pranavtendolkr/horizon,wolverineav/horizon,idjaw/horizon,bigswitch/horizon,watonyweng/horizon,coreycb/horizon,icloudrnd/automation_tools,VaneCloud/horizon,watonyweng/horizon,mandeepdhami/horizon,django-leonardo/horizon,NeCTAR-RC/horizon,bigswitch/horizon,orbitfp7/horizon,Hodorable/0602,xinwu/horizon,gerrive/horizon,RudoCris/horizon,j4/horizon,CiscoSystems/avos,FNST-OpenStack/horizon,Solinea/horizon,VaneCloud/horizon,froyobin/horizon,tqtran7/horizon,blueboxgroup/horizon,anthonydillon/horizon,Solinea/horizon,tsufiev/horizon,django-leonardo/horizon,FNST-OpenStack/horizon,karthik-suresh/horizon,bac/horizon,mrunge/openstack_horizon,dan1/horizon-x509,ChameleonCloud/horizon,endorphinl/horizon,ChameleonCloud/horizon,eayunstack/horizon,karthik-suresh/horizon,saydulk/horizon,RudoCris/horizon,mrunge/horizon,NCI-Cloud/horizon,pranavtendolkr/horizon,luhanhan/horizon,maestro-hybrid-cloud/horizon,tellesnobrega/horizon,doug-fish/horizon,gerrive/horizon,mrunge/openstack_horizon,davidcusatis/horizon,blueboxgroup/horizon,zouyapeng/horizon,noironetworks/horizon,liyitest/rr,RudoCris/horizon,Metaswitch/horizon,agileblaze/OpenStackTwoFactorAuthentication,idjaw/horizon,mrunge/horizon_lib,wangxiangyu/horizon,endorphinl/horizon,agileblaze/OpenStackTwoFactorAuthentication,ging/horizon,wolverineav/horizon,yeming233/horizon,ging/horizon,davidcusatis/horizon,endorphinl/horizon,endorphinl/horizon-fork,openstack/horizon,anthonydillon/horizon,Solinea/horizon,j4/horizon,idjaw/horizon,xme1226/horizon,damien-dg/horizon,pranavtendolkr/horizon,Daniex/horizon,doug-fish/horizon,saydulk/horizon,vladryk/horizon,endorphinl/horizon-fork,tellesnobrega/horizon,flochaz/horizon,kfox1111/horizon,bac/horizon,eayunstack/horizon,redhat-cip/horizon,NeCTAR-RC/horizon,openstack/horizon,icloudrnd/automation_tools,mdavid/horizon,flochaz/horizon,bigswitch/horizon,mandeepdhami/horizon,luhanhan/horizon,tsufiev/horizon,NCI-Cloud/horizon,Dark-Hacker/horizon,idjaw/horizon,noironetworks/horizon,takeshineshiro/horizon,gerrive/horizon,FNST-OpenStack/horizon,vladryk/horizon,mandeepdhami/horizon,liyitest/rr,Mirantis/mos-horizon,CiscoSystems/horizon,izadorozhna/dashboard_integration_tests,davidcusatis/horizon,damien-dg/horizon,kfox1111/horizon,kfox1111/horizon,damien-dg/horizon,ging/horizon,izadorozhna/dashboard_integration_tests,karthik-suresh/horizon,Solinea/horizon,bigswitch/horizon,agileblaze/OpenStackTwoFactorAuthentication