perf build: Rename CORE_FEATURE_TESTS to FEATURE_TESTS

perf build: Rename CORE_FEATURE_TESTS to FEATURE_TESTS

Preparing for feature checks separation, moving related stuff under
'FEATURE*' namespace.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <david.ahern@oracle.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-iobj4f9gygcakrk2v5u61159@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>