Merge PR MPAS-Dev#274 'xylar/ocean/update_BGC_python3' into ocean/dev…

…elop

The only change is the addition of python 3 support during the
build.

Brings in E3SM-Project/Ocean-BGC#1 and
E3SM-Project/Ocean-BGC#2.

src/core_ocean/get_BGC.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 ## BGC Tag for build
-BGC_TAG=2b8aadd
+BGC_TAG=5588636f0e71a97c532391a5d9c252b1c6f3611a
 
 ## Subdirectory in BGC repo to use
 BGC_SUBDIR=.