Invalid ovs bridge is created if multiple bridges are defined by role specific NeutronBridgeMappings

Issue

• The NeutronBridgeMappings parameter is defined as part of role specific parameters and have a string value defining multiple bridge mappings

parameter_defaults:
  ComputeParameters:
    NeutronBridgeMappings: 'datacentre:br-ex,datacentre2:br-ex2'

• After deployment is completed, an invalid ovs bridge is created in overcloud nodes

[root@compute-0 ~]$ sudo ovs-vsctl -t5 show
...
    Bridge "br-ex,datacentre2"
        Port "br-ex,datacentre2"
            Interface  "br-ex,datacentre2"
                type: internal
                ...