Fix issue #2336 - honor the -C arg to ctest. Honor it for all stages of running -D dashboards from the command line and running ctest_configure, ctest_build and ctest_test commands in -S scripts. Also, allow a script to change it by setting the CTEST_CONFIGURATION_TYPE variable: allows for multiple configuration build/test cycles within one script. Add a new signature for the cmake command build_command that accepts CONFIGURATION as one argument. The original build_command signature is still there, but now marked as deprecated in the documentation. Of course... also add CTestConfig tests to verify that -C is honored for -D dashboards and -S scripts.