Error in writing out r4 real data

This is with release-cesm2.0.01 which brings in a change to write out real data as r4 instead of everything being r8.

The following tests fail:

ERP_Ld5.f10_f10_musgs.I2000Clm50Vic.cheyenne_gnu.clm-decStart.GC.release-clm5009chgnua
ERP_P36x2_D_Ld5.f10_f10_musgs.I1850Clm45Bgc.cheyenne_gnu.clm-default.GC.release-clm5009chgnua
ERP_P36x2_D_Ld5.f10_f10_musgs.I1850Clm45BgcCru.cheyenne_intel.clm-default.GC.release-clm5009chintela
ERP_P36x2_D_Ld5.f10_f10_musgs.I2000Clm45Sp.cheyenne_intel.clm-default.GC.release-clm5009chintela
ERP_P36x2_D_Ld5.f10_f10_musgs.IHistClm45BgcCruGs.cheyenne_intel.clm-decStart.GC.release-clm5009chintela
ERS_Ly5_P72x1.f10_f10_musgs.IHistClm45BgcCrop.cheyenne_intel.clm-cropMonthOutput.GC.release-clm5009chintela

The fail looks like:

```
1: pio_support::pio_die:: myrank= -1 : ERROR:
1: pionfwrite_mod::write_nfdarray_real: 250 :
1: NetCDF: Numeric conversion not representable
37: pionfwrite_mod::write_nfdarray_real 107 IAM: 1 start:
37: 1 181 count: 720
37: 180 size : 1 error: -60
37: 598 0
37: pio_support::pio_die:: myrank= -1 : ERROR:
37: pionfwrite_mod::write_nfdarray_real: 250 :
37: NetCDF: Numeric conversion not representable
1:Image PC Routine Line Source
1:cesm.exe 00000000019272AD Unknown Unknown Unknown
1:cesm.exe 000000000124DAA1 pio_support_mp_pi 118 pio_support.F90
1:cesm.exe 000000000124BC51 pio_utils_mp_chec 59 pio_utils.F90
1:cesm.exe 000000000134E9DA pionfwrite_mod_mp 250 pionfwrite_mod.F90.in
1:cesm.exe 000000000130D2AA piodarray_mp_writ 650 piodarray.F90.in
1:cesm.exe 000000000130FF51 piodarray_mp_writ 221 piodarray.F90.in
1:cesm.exe 0000000000C93F30 rtmio_mp_ncd_io_r 1825 RtmIO.F90
1:cesm.exe 0000000000C86EF0 rtmhistfile_mp_ht 930 RtmHistFile.F90
1:cesm.exe 0000000000C8476C rtmhistfile_mp_rt 1099 RtmHistFile.F90
1:cesm.exe 0000000000CA0ED9 rtmmod_mp_rtmrun_ 1309 RtmMod.F90
1:cesm.exe 0000000000C795A8 rof_comp_mct_mp_r 298 rof_comp_mct.F90
1:cesm.exe 0000000000424B34 component_mod_mp_ 728 component_mod.F90
1:cesm.exe 000000000040A369 cime_comp_mod_mp_ 2675 cime_comp_mod.F90
1:cesm.exe 0000000000424862 MAIN__ 103 cime_driver.F90
1:cesm.exe 000000000040829E Unknown Unknown Unknown
1:libc-2.19.so 00002AAAB04DCB25 __libc_start_main Unknown Unknown
1:cesm.exe 00000000004081A9 Unknown Unknown Unknown
1:MPT ERROR: Rank 1(g:1) is aborting with error code 1.

```

The problem is likely that there are nans that are trying to be converted to real(r4), and it can't do that.