ctsm warm_start mods

[jtruesdal]

The following mods allow ctsm interpolation of a 2d grid to a single gridcell for pts mode. They are required to get I compsets passing with the new SE grid as well as allow a CTSM warm start when running CAM in single column mode.

[jtruesdal]

With the latest fix CLM now can restart in single column mode with SCAM and using the CAM SCT regression test it is BFB with a 3D CAM run. @slevis-lmwg could you run the standard clm regression tests on a merged up sandbox of this PR to make sure I didn't break anything on the land side with this update. I have CAM mods that will go along with this to add the new scam SCT test for checking BFB with warmstarts of CLM.

[slevis-lmwg]

Note to self before I start testing: Confirm that we have ne3 test(s) in clm's test-suites

[slevis-lmwg]

aux_clm has this ne3_ne3 test on both derecho and izumi
<test name="SMS_D_Ld1_Mmpi-serial" grid="ne3_ne3_mg37" compset="I2000Clm50SpRs" testmods="clm/ptsRLA">
aux_clm also has this ne3_ne3 test on izumi
<test name="SMS_D_Ld1_Mmpi-serial" grid="ne3_ne3_mg37" compset="I2000Clm50SpRs" testmods="clm/ptsROA">

I think that these are the ne3 tests that we intended to have in there, so I will start aux_clm on both derecho and izumi:
./run_sys_tests -s aux_clm -c ctsm5.3.009 --skip-generate