perf stat: Add missing aggregation headers for --metric-only CSV

perf stat: Add missing aggregation headers for --metric-only CSV

When in CSV mode --metric-only outputs an header, unlike the other
modes. Previously it did not properly print headers for the aggregation
columns, so the headers were actually shifted against the real values.

Fix this here by outputting the correct headers for CSV.

v2: Indent array.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1464119559-17203-4-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>