Merge commit 'v2.5.1' into devel-2.5

Merge commit 'v2.5.1' into devel-2.5

* commit 'v2.5.1':
  Update NEWS and bump version for 2.5.1 release
  Fix gnt-group --help display
  Fix hardcoded Xen kernel path
  Fix grow-disk handling of invalid units
  Accept both PUT and POST in noded
  Preserve bridge MTU in KVM ifup script
  Update synopsis for “gnt-cluster repair-disk-sizes”
  Reconcile Makefile.am and test data files
  Workaround changed LVM behaviour
  Enable lvmstrap to run under Linux 3.x
  Add a default PATH variable to OS scripts env
  Move hooks PATH environment variable to constants
  Add note to the install doc about bridge MAC issues
  Fix exception re-raising in Python Luxi clients
  Fix LVM volume listing with newer LVM

Conflicts:
        lib/client/gnt_group.py (trivial, fixup conflicts from 6bc3ed14)

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>