Enable lvmstrap to run under Linux 3.x

Extend the kernel version check to also accept Linux 3.x as valid.

Signed-off-by: Alexander Schreiber <als@google.com>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

tools/lvmstrap

@@ -272,9 +272,9 @@ def CheckPrereq():
     raise PrereqError("This tool only runs on Linux"
                       " (detected OS: %s)." % osname)
 
-  if not release.startswith("2.6."):
+  if not (release.startswith("2.6.") or release.startswith("3.")):
     raise PrereqError("Wrong major kernel version (detected %s, needs"
-                      " 2.6.*)" % release)
+                      " 2.6.* or 3.*)" % release)
 
   if not os.path.ismount("/sys"):
     raise PrereqError("Can't find a filesystem mounted at /sys."