Provide backward compatiblity for old style method.

Thanks to partially reverting "Use only externally provided buildout."
(commit 2a0bbcc9) it is possible to use
slapgrid with provided buildout binary, but no one is forced to follow this
way, as old style internal bootstraping procedure is available.

Conflicts, manually merged:

	slapos/grid/slapgrid.py
	slapos/grid/utils.py

slapos/grid/utils.py

@@ -27,6 +27,7 @@
 import logging
 import hashlib
 import os
+import pkg_resources
 import stat
 import subprocess
 import sys
@@ -216,8 +217,8 @@ def dropPrivileges(uid, gid):
   logger.info('Succesfully dropped privileges to uid=%r gid=%r' % (uid, gid))
 
 
-def bootstrapBuildout(path, buildout, additional_buildout_parametr_list=None,
-    console=False):
+def bootstrapBuildout(path, buildout=None,
+    additional_buildout_parametr_list=None, console=False):
   if additional_buildout_parametr_list is None:
     additional_buildout_parametr_list = []
   logger = logging.getLogger('BuildoutManager')
@@ -227,7 +228,13 @@ def bootstrapBuildout(path, buildout, additional_buildout_parametr_list=None,
   gid = stat_info.st_gid
 
   invocation_list = [sys.executable, '-S']
-  invocation_list.append(buildout)
+  if buildout is not None:
+    invocation_list.append(buildout)
+  else:
+    logger.warning('Using old style bootstrap of included bootstrap file. '
+      'Consider setting buildout binary location.')
+    invocation_list.append(pkg_resources.resource_filename(__name__,
+      'zc.buildout-bootstap.py'))
   invocation_list.extend(additional_buildout_parametr_list)
   invocation_list.append('bootstrap')
   try: