perf tests: Fix record+probe_libc_inet_pton.sh when event exists

perf tests: Fix record+probe_libc_inet_pton.sh when event exists

If the event 'probe_libc:inet_pton' already exists, this test fails and
deletes the existing event before exiting. This will then pass for any
subsequent executions.

Instead of skipping to deleting the existing event because of failing to
add a new event, a duplicate event is now created and the script
continues with the usual checks. Only the new duplicate event that is
created at the beginning of the test is deleted as a part of the
cleanups in the end. All existing events remain as it is.

This can be observed on a powerpc64 system running Fedora 27 as shown
below.

  # perf probe -x /usr/lib64/power8/libc-2.26.so -a inet_pton

  Added new event:
    probe_libc:inet_pton (on inet_pton in /usr/lib64/power8/libc-2.26.so)

Before:

  # perf test -v "probe libc's inet_pton & backtrace it with ping"

  62: probe libc's inet_pton & backtrace it with ping       :
  --- start ---
  test child forked, pid 21302
  test child finished with -1
  ---- end ----
  probe libc's inet_pton & backtrace it with ping: FAILED!

  # perf probe --list

After:

  # perf test -v "probe libc's inet_pton & backtrace it with ping"

  62: probe libc's inet_pton & backtrace it with ping       :
  --- start ---
  test child forked, pid 21490
  ping 21513 [035] 39357.565561: probe_libc:inet_pton_1: (7fffa4c623b0)
  7fffa4c623b0 __GI___inet_pton+0x0 (/usr/lib64/power8/libc-2.26.so)
  7fffa4c190dc gaih_inet.constprop.7+0xf4c (/usr/lib64/power8/libc-2.26.so)
  7fffa4c19c4c getaddrinfo+0x15c (/usr/lib64/power8/libc-2.26.so)
  111d93c20 main+0x3e0 (/usr/bin/ping)
  test child finished with 0
  ---- end ----
  probe libc's inet_pton & backtrace it with ping: Ok

  # perf probe --list

    probe_libc:inet_pton (on __inet_pton@resolv/inet_pton.c in /usr/lib64/power8/libc-2.26.so)

Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kim Phillips <kim.phillips@arm.com>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/e11fecff96e6cf4c65cdbd9012463513d7b8356c.1530724939.git.sandipan@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>