Regression test portability: batch of bugs (volume 2)

Fix various regression test portability in tests/bugs.

bug-861542.t
- Avoid syntax specific to GNU sed.

bug-860663.t
- Command argument length is system dependent, and specifying 1000 file
  path may overflow it. Use a C program to do the job in a portable and
  efficient way.
- Add a test that we created the specified amount of files.

bug-858242.c, bug-808400-fcntl.c, bug-808400-flock.c
- fstat64() is Linux-specific. Define it as fstat for other systems.

bug-823081.t
- Use portable tail -n instead of tail --lines

In many tests:
- Do not assume python interpreter name. Use $PYTHON as defined
  in env.rc by configure.

utils/libcxattr.py
- If python version is 2.6 or higher, use a portable mechanism to
  recover errno. The original version is retained for python version
  2.5 and earlier but it only works on Linux.

BUG: 1129939
Change-Id: If2fea1ffec5cc6ab2de426fb200e884450afe61b
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/9097
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>