Adding to tests that aims on kernel breakpoint modification bugs.

First test creates HW breakpoint, tries to change it and checks it was
properly changed. It aims on kernel issue that prevents HW breakpoint to
be changed via ptrace interface.

The first test forks, the child sets itself as ptrace tracee and waits
in signal for parent to trace it, then it calls bp_1 and quits.

The parent does following steps:

 - creates a new breakpoint (id 0) for bp_2 function
 - changes that breakpoint to bp_1 function
 - waits for the breakpoint to hit and checks
   it has proper rip of bp_1 function

This test aims on an issue in kernel preventing to change disabled
breakpoints

Second test mimics the first one except for few steps
in the parent:
 - creates a new breakpoint (id 0) for bp_1 function
 - changes that breakpoint to bogus (-1) address
 - waits for the breakpoint to hit and checks
   it has proper rip of bp_1 function

This test aims on an issue in kernel disabling enabled
breakpoint after unsuccesful change.

Committer testing:

  # uname -a
  Linux jouet 4.18.0-rc8-00002-g1236568e #12 SMP Tue Aug 7 14:08:26 -03 2018 x86_64 x86_64 x86_64 GNU/Linux
  # perf test -v "bp modify"
  62: x86 bp modify                                         :
  --- start ---
  test child forked, pid 25671
  in bp_1
  tracee exited prematurely 2
  FAILED arch/x86/tests/bp-modify.c:209 modify test 1 failed

  test child finished with -1
  ---- end ----
  x86 bp modify: FAILED!
  #
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Milind Chabbi <chabbi.milind@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180827091228.2878-2-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>