have uniform uprobe event names for python and C++

have uniform uprobe event names for python and C++

This is a followup change for previous commit 0ba15075fc5f
(permit multiple pids attaching to the same probe).
That commit changes the event name for python uprobe API
in order to permit multiple processes attaching to the
same uprobe point. The C++ uprobe event name remains
unchanged and thus a descrepancy.

This patch add changes to C++ side and also make python uretprobe
having the same naming convention.

Originally I experimented to put the common code to generate
event names in libbpf.c. But doing this seems more klunky
than simplicity of C++ and Python. So I stick to the current
design.

No need to add pid to kprobe event names as kprobe bpf invocation
will ignore pid anyway.

Signed-off-by: Yonghong Song <yhs@fb.com>