Workaround openrc failure on zsh
Workaround openrc failure on zsh

The recent GIT_DEPTH change introduced a [[ ]] construct
which doesn't work for zsh 5.0.2.  Workaround it by tweaking the test.

The following is a demonstration to show how zsh behaves:

    % if [[ "" ]];then echo hoge;fi
    zsh: parse error near `]]'
    % if [[ "x" ]];then echo hoge;fi
    zsh: parse error near `]]'
    % if [[ -n "" ]];then echo hoge;fi
    % if [[ -n "x" ]];then echo hoge;fi
    hoge
    %

Closes-Bug: #1387943
Change-Id: Ia88de876dacb3664a7c3d8f5a035e8e50fddb678

richliu/devstack,j4/devstack,sc68cal/devstack,bljgaurav/openstack-test,bswartz/devstack,noironetworks/devstack,affo/devstack,LoHChina/devstack,ozamiatin/devstack,wenhuizhang/devstack,neerja28/Devstack_GlusterFS,prithivm/branch01,bigswitch/devstack,dirkmueller/devstack,noironetworks/devstack,upadhyay-prashant/devstack,nawawi/openstack,costingalan/devstack,group-policy/devstack,bswartz/devstack,pczerkas/devstack,dtroyer/devstack,samgoon/devstack,affo/devstack,TwinkleChawla/devstack,vishnugonela/devstack,LoHChina/devstack,NaokiMiyata/devstack,costingalan/devstack,olivierlemasle/devstack,olivierlemasle/devstack,flavio-fernandes/devstack,atulpatil301/devstack,nuxeh/devstack,flavio-fernandes/devstack,kplus/devstack-moonshot,eharney/devstack,andrewrothstein/devstack,TwinkleChawla/devstack,promptworks/devstack,varunarya10/devstack,HPCHub/devstack,mmasaki/devstack,herrsechs/devstack,Mahito/devstack,mc2014/devstack,thomasem/devstack,NaokiMiyata/devstack,CloudServer/devstack,vsham20/devstack,sc68cal/devstack,bigswitch/devstack,sequenceiq/devstack,pacinete/devstack,atulpatil301/devstack,BSJAIN92/OpenStack,mc2014/devstack,rushiagr/devstack,prithivm/branch01,sequenceiq/devstack,samgoon/devstack,bq-xiao/devstack,neerja28/Devstack_GlusterFS,CloudServer/devstack,bq-xiao/devstack,pombredanne/devstack,mssumanth/devstack,varunarya10/devstack,liuquansheng47/devstack,pczerkas/devstack,avvocatodemarchis/devstack,ozamiatin/devstack,upadhyay-prashant/devstack,promptworks/devstack,mmasaki/devstack,thomasem/devstack,wenhuizhang/devstack,HPCHub/devstack,Mahito/devstack,pacinete/devstack,dtroyer/devstack,bljgaurav/openstack-test,parul24/devstack,rushiagr/devstack,nawawi/openstack,openstack-dev/devstack,parul24/devstack,herrsechs/devstack,vsham20/devstack,mssumanth/devstack,andrewrothstein/devstack,group-policy/devstack,j4/devstack,BSJAIN92/OpenStack,avvocatodemarchis/devstack,dirkmueller/devstack,pombredanne/devstack,richliu/devstack,kplus/devstack-moonshot,nuxeh/devstack,openstack-dev/devstack,vishnugonela/devstack,eharney/devstack,liuquansheng47/devstack