perf tools: Force period term to overload global settings

Currently the command line option settings beats the per event period
settings:

With no global settings, we get per-event configuration:

  $ perf record -e 'cpu/instructions,period=20000/' sleep 1
  $ perf evlist -v
  ... { sample_period, sample_freq }: 20000 ...

With 'c' option period setup, we get 'c' option value:
  $ perf record -e 'cpu/instructions,period=20000/' -c 1000 sleep 1
  $ perf evlist -v
  ... { sample_period, sample_freq }: 1000 ...

This patch makes the per-event settings overload the global 'c' option
setup:

  $ perf record -e 'cpu/instructions,period=20000/' -c 1000 sleep 1
  $ perf evlist -v
  ... { sample_period, sample_freq }: 20000 ...

I think the making the per-event settings to overload any other config
makes more sense than current state. However it breaks the current
'period' term handling, which might cause some noise.. so let's see ;-).

Also fixing parse event tests with the new behaviour.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1438162936-59698-3-git-send-email-kan.liang@intel.com
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 63ee040..ac41350 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -46,7 +46,7 @@
           /sys/bus/event_sources/devices/<pmu>/format/*
 
 	  There are also some params which are not defined in .../<pmu>/format/*.
-	  These params can be used to set event defaults.
+	  These params can be used to overload default config values per event.
 	  Here is a list of the params.
 	  - 'period': Set event sampling period