Print choices in the config generator
Print choices in the config generator

One more stop-gap till we move Nova to oslo-config-generator. Copy
a bit of code to print the Allowed values in a StrOpt's choices
field.

Change-Id: I1ba69084e385fccbb54321a50500604393f886be

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