always use python3

because columnstore uses python3, so rocksdb can be picky too.
python3 is present in all supported distros.
and python2 is obsolete anyway.

CMakeLists.txt

@@ -425,7 +425,7 @@ INCLUDE(mariadb_connector_c) # this does ADD_SUBDIRECTORY(libmariadb)
 INCLUDE(cpack_rpm)
 INCLUDE(cpack_deb)
 
-SET(PYTHON_SHEBANG "/usr/bin/env python" CACHE STRING "python shebang")
+SET(PYTHON_SHEBANG "/usr/bin/env python3" CACHE STRING "python shebang")
 MARK_AS_ADVANCED(PYTHON_SHEBANG)
 
 # Add storage engines and plugins.

cmake/cpack_deb.cmake

@@ -6,5 +6,6 @@ IF(DEB)
 SET(CPACK_COMPONENT_SERVER_GROUP "server")
 SET(CPACK_COMPONENT_README_GROUP "server")
 SET(CPACK_COMPONENTS_ALL Server Test SharedLibraries)
+SET(PYTHON_SHEBANG "/usr/bin/python3" CACHE STRING "python shebang")
 ENDIF(DEB)
 

cmake/cpack_rpm.cmake

@@ -249,9 +249,7 @@ ELSEIF(RPM MATCHES "sles")
     "mariadb-server = %{version}-%{release}"
   )
 ENDIF()
-IF(RPM MATCHES "fedora31" OR RPM MATCHES "(rhel|centos)8")
-  SET(PYTHON_SHEBANG "/usr/bin/python3" CACHE STRING "python shebang")
-ENDIF()
+SET(PYTHON_SHEBANG "/usr/bin/python3" CACHE STRING "python shebang")
 
 # If we want to build build MariaDB-shared-compat,
 # extract compat libraries from MariaDB-shared-5.3 rpm