git-gerrit-push: Append topic to refspecs instead of overwriting
git-gerrit-push: Append topic to refspecs instead of overwriting

Other logic may later be added to add more refspecs.

mspark93/VTK,kaspermarstal/SimpleElastix,jmerkow/VTK,blowekamp/SimpleITK,sankhesh/VTK,demarle/VTK,sankhesh/VTK,InsightSoftwareConsortium/SimpleITK,richardbeare/SimpleITK,msmolens/VTK,msmolens/VTK,sumedhasingla/VTK,sankhesh/VTK,sankhesh/VTK,mspark93/VTK,msmolens/VTK,keithroe/vtkoptix,msmolens/VTK,SimVascular/VTK,SimVascular/VTK,InsightSoftwareConsortium/SimpleITK,demarle/VTK,richardbeare/SimpleITK,keithroe/vtkoptix,blowekamp/SimpleITK,gram526/VTK,SimpleITK/SimpleITK,msmolens/VTK,candy7393/VTK,candy7393/VTK,blowekamp/SimpleITK,SimVascular/VTK,candy7393/VTK,sumedhasingla/VTK,SimVascular/VTK,sumedhasingla/VTK,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,gram526/VTK,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,richardbeare/SimpleITK,sumedhasingla/VTK,jmerkow/VTK,richardbeare/SimpleITK,richardbeare/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,jmerkow/VTK,kaspermarstal/SimpleElastix,InsightSoftwareConsortium/SimpleITK,gram526/VTK,SimpleITK/SimpleITK,blowekamp/SimpleITK,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,msmolens/VTK,SimpleITK/SimpleITK,sankhesh/VTK,InsightSoftwareConsortium/SimpleITK,mspark93/VTK,sumedhasingla/VTK,demarle/VTK,SimpleITK/SimpleITK,jmerkow/VTK,SimVascular/VTK,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,sankhesh/VTK,demarle/VTK,mspark93/VTK,keithroe/vtkoptix,blowekamp/SimpleITK,mspark93/VTK,SimpleITK/SimpleITK,sankhesh/VTK,mspark93/VTK,keithroe/vtkoptix,jmerkow/VTK,demarle/VTK,richardbeare/SimpleITK,mspark93/VTK,kaspermarstal/SimpleElastix,msmolens/VTK,sumedhasingla/VTK,candy7393/VTK,jmerkow/VTK,candy7393/VTK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,InsightSoftwareConsortium/SimpleITK,richardbeare/SimpleITK,gram526/VTK,gram526/VTK,candy7393/VTK,demarle/VTK,blowekamp/SimpleITK,jmerkow/VTK,sumedhasingla/VTK,gram526/VTK,mspark93/VTK,gram526/VTK,msmolens/VTK,keithroe/vtkoptix,blowekamp/SimpleITK,sankhesh/VTK,gram526/VTK,InsightSoftwareConsortium/SimpleITK,candy7393/VTK,demarle/VTK,SimVascular/VTK,demarle/VTK,kaspermarstal/SimpleElastix,candy7393/VTK,jmerkow/VTK,SimpleITK/SimpleITK