tox.ini: Avoid using bash where unnecessary
tox.ini: Avoid using bash where unnecessary

Switch to sh, which is hopefully more ubiquitously available than bash.

A recent change (commit 085a35d657cf0fa41a402f2af66c4beaa0f60db2)
introduced bash dependency for "tox -e pep8".  It broke my environment,
where bash is not available.  This change aims to restore it.
As far as I undestand, the change in question doesn't actually need
the specific shell dialect.  So switch to sh, which is expected to be
available for any POSIX-like systems, would improve the situation.

Closes-Bug: #1382327
Change-Id: Ie023d2265d9949a3e3721f03e865e4acfb460de2

paninetworks/neutron,barnsnake351/neutron,bigswitch/neutron,waltBB/neutron_read,aristanetworks/neutron,bgxavier/neutron,mahak/neutron,Metaswitch/calico-neutron,openstack/neutron,magic0704/neutron,leeseuljeong/leeseulstack_neutron,huntxu/neutron,yuewko/neutron,CiscoSystems/neutron,eayunstack/neutron,dims/neutron,gkotton/neutron,gkotton/neutron,sasukeh/neutron,SmartInfrastructures/neutron,dims/neutron,sasukeh/neutron,pnavarro/neutron,dhanunjaya/neutron,cloudbase/neutron,leeseuljeong/leeseulstack_neutron,leeseulstack/openstack,rdo-management/neutron,wolverineav/neutron,leeseuljeong/leeseulstack_neutron,eayunstack/neutron,glove747/liberty-neutron,jumpojoy/neutron,takeshineshiro/neutron,neoareslinux/neutron,leeseulstack/openstack,bigswitch/neutron,silenci/neutron,klmitch/neutron,Stavitsky/neutron,yanheven/neutron,yuewko/neutron,barnsnake351/neutron,vivekanand1101/neutron,mmnelemane/neutron,NeCTAR-RC/neutron,apporc/neutron,glove747/liberty-neutron,mmnelemane/neutron,JianyuWang/neutron,miyakz1192/neutron,mandeepdhami/neutron,sebrandon1/neutron,silenci/neutron,Stavitsky/neutron,igor-toga/local-snat,noironetworks/neutron,alexandrucoman/vbox-neutron-agent,huntxu/neutron,SmartInfrastructures/neutron,dhanunjaya/neutron,noironetworks/neutron,SamYaple/neutron,mahak/neutron,klmitch/neutron,apporc/neutron,neoareslinux/neutron,aristanetworks/neutron,adelina-t/neutron,skyddv/neutron,cloudbase/neutron,antonioUnina/neutron,openstack/neutron,magic0704/neutron,swdream/neutron,watonyweng/neutron,mandeepdhami/neutron,javaos74/neutron,projectcalico/calico-neutron,miyakz1192/neutron,yanheven/neutron,wenhuizhang/neutron,swdream/neutron,infobloxopen/neutron,JianyuWang/neutron,bgxavier/neutron,rdo-management/neutron,wolverineav/neutron,SamYaple/neutron,watonyweng/neutron,blueboxgroup/neutron,leeseulstack/openstack,skyddv/neutron,MaximNevrov/neutron,sebrandon1/neutron,wenhuizhang/neutron,mattt416/neutron,chitr/neutron,MaximNevrov/neutron,asgard-lab/neutron,JioCloud/neutron,cloudbase/neutron-virtualbox,gkotton/neutron,suneeth51/neutron,jacknjzhou/neutron,asgard-lab/neutron,vivekanand1101/neutron,mattt416/neutron,infobloxopen/neutron,cisco-openstack/neutron,blueboxgroup/neutron,paninetworks/neutron,jerryz1982/neutron,vveerava/Openstack,shahbazn/neutron,eonpatapon/neutron,alexandrucoman/vbox-neutron-agent,antonioUnina/neutron,blueboxgroup/neutron,cloudbase/neutron-virtualbox,JioCloud/neutron,waltBB/neutron_read,adelina-t/neutron,vveerava/Openstack,jumpojoy/neutron,vveerava/Openstack,pnavarro/neutron,chitr/neutron,shahbazn/neutron,projectcalico/calico-neutron,openstack/neutron,NeCTAR-RC/neutron,CiscoSystems/neutron,jacknjzhou/neutron,suneeth51/neutron,eonpatapon/neutron,igor-toga/local-snat,jerryz1982/neutron,cisco-openstack/neutron,CiscoSystems/neutron,Metaswitch/calico-neutron,javaos74/neutron,takeshineshiro/neutron,mahak/neutron