CMake Prepare for alternate core selections

[islas]

TYPE: enhancement

KEYWORDS: cmake, wrfplus, da

SOURCE: internal

DESCRIPTION OF CHANGES:
Problem:
The current CMake build only works with the em core / ARW in mind and presents a non-intuitive selection when attempting other cores. While these cores are not yet supported in the CMake build, remove these selections sets up the configuration script to be able to present a familiar set of options.

Solution:
Remove normally unselectable options from configure_new after selecting non-ARW cores. Put in place stand-in values for these unselected variables.

[islas]

Requires #2056 and #2053

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None

[amstokely]

Looks good to me, and I approve these changes.

*Note: My review is based on my general experience with CMake and Python, as I haven’t personally used WRF.