Logic for convective transportable tracers needs to be improved

[climbfuji]

Description

I am submitting this as a bug report, although it is to some extend a necessaary cleanup and not a bug.

Convective transportable tracers are assembled in a clw array (standard name convective_transportable_tracers) in scheme GFS_suite_interstitial_3_run. Depending on the microphysics scheme, either one or two tracers are used in the clw array. If only one is used, the other entry gets set to -999 (which tells the convection schemes to do something different than if there are two tracers).

The corresponding logic to update the second, missing tracer from -999 to zero is currently at the end of GFS_SCNV_generic_post_run. This is not the correctt place, it belongs at the beginning of GFS_suite_interstitial_4_run so that when a user decides to skip deep and shallow convection, the following code will still work:

      ...
      <scheme>get_phi_fv3</scheme>
      <scheme>GFS_suite_interstitial_3</scheme>
      <!-- Comment out entire deep/shallow convection block
      <scheme>GFS_DCNV_generic_pre</scheme>
      <scheme>samfdeepcnv</scheme>
      <scheme>GFS_DCNV_generic_post</scheme>
      <scheme>GFS_SCNV_generic_pre</scheme>
      <scheme>samfshalcnv</scheme>
      <scheme>GFS_SCNV_generic_post</scheme>
      -->
      <scheme>GFS_suite_interstitial_4</scheme>
      <scheme>cnvc90</scheme>
      ...