Shorten some currently very long debug tests

[billsacks]

These two debug tests take a long time to run (~ 1.5 hours): ERP_D_Lm9.f10_f10_musgs.IHistClm50BgcCrop.cheyenne_intel.clm-ciso_monthly and SMS_D_Lm13.f10_f10_musgs.IHistClm50BgcCrop.cheyenne_intel.clm-ciso_monthly. Tracing the history of these tests: I had introduced a short decStart transient test with isotopes: ERP_D_P15x2.f10_f10_musgs.IHistClm50Bgc.yellowstone_intel.clm-ciso_decStart, then, in clm4_5_16_r255 (which fixed some C isotope things), @ekluzek introduced something like the above tests (though, at the time, one was on yellowstone and one was on cheyenne). This is also when #177 was found - so maybe he lengthened these to test this issue?

I question whether it's really worth having such long debug tests in the test suite. I guess I can be convinced that there is some value in having a single long debug test in the test suite, but at the very least I'd like to remove this long ERP debug test, replacing it with something like: ERP_D_Ld10_P36x2.f10_f10_musgs.IHistClm50Bgc.cheyenne_intel.clm-ciso_decStart (which is much shorter and covers the crossing of the year boundary).

[billsacks]

Actually, I see that we already have something like my suggested ciso_decStart test, which also includes crops: ERP_D_Ld10.f10_f10_musgs.IHistClm50BgcCrop.cheyenne_intel.clm-ciso_decStart. So I'd suggest dropping ERP_D_Lm9.f10_f10_musgs.IHistClm50BgcCrop.cheyenne_intel.clm-ciso_monthly and just making that existing ciso_decStart test include threading, by adding P36x2.