perf stat has a --delay option to delay measuring the workload.

This is useful to skip measuring the startup phase of the program, which
is often very different from the main workload.

The same is useful for perf record when sampling.

--no-delay was already taken, so add a --initial-delay
to perf record too.
-D was already taken for record, so there is only a long option.

v2: Don't disable group members (Namhyung Kim)
v3: port to latest perf/core
    rename to --initial-delay to avoid conflict with --no-delay
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NNamhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1389476307-2124-1-git-send-email-andi@firstfloor.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>