perf tools: Improve Python feature detection messages

Change the Python detection message from:

  config/Makefile:566: No python-config tool was found
  config/Makefile:566: Python support will not be built

  config/Makefile:565: No 'python-config' tool was found: disables Python support - please install python-devel/python-dev

It's now a standard one-line message with a package install suggestion,
and it also uses the standard language used by other feature detection
messages.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <david.ahern@oracle.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150228083345.GB31887@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>