LU-5740 build: add RHEL6.6 [2.6.32-504.el6] to build selections

Add support for building with RHEL6.6 kernel version 2.6.32-504.el6
while retaining the ability to build with older RHEL 6.5 kernels.
New ldiskfs patch series for el6.6 is included.

Test-Parameters: clientdistro=el6.6 mdsdistro=el6.6\
  ossdistro=el6.6 mdsfilesystemtype=ldiskfs\
  mdtfilesystemtype=ldiskfs ostfilesystemtype=ldiskfs

Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Change-Id: I780feefbbc179607762c0d2997fd608830f3db8b
Reviewed-on: http://review.whamcloud.com/12609
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Reviewed-by: Minh Diep <minh.diep@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>