[Xend/ACM] Provide explicit initialization function for bootloader class

This patch refactors the initialization code for the bootloader class
and puts it into an explicit initialization function that is called
from another class.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>

tools/python/xen/util/bootloader.py

@@ -26,8 +26,6 @@ from xen.xend.XendLogging import log
 from xen.util import mkdir
 import xen.util.xsm.xsm as security
 
-__bootloader = None
-
 #
 # Functions for modifying entries in the bootloader, i.e. adding
 # a module to boot the system with a policy.
@@ -513,8 +511,11 @@ class LatePolicyLoader(Bootloader):
         Bootloader.__init__(self)
 
     def probe(self):
-        _dir=os.path.dirname(self.FILENAME)
-        mkdir.parents(_dir, stat.S_IRWXU)
+        try:
+            _dir=os.path.dirname(self.FILENAME)
+            mkdir.parents(_dir, stat.S_IRWXU)
+        except:
+            return False
         return True
 
     def get_default_title(self):
@@ -614,10 +615,12 @@ class LatePolicyLoader(Bootloader):
 
 __bootloader = Bootloader()
 
-grub = Grub()
-if grub.probe() == True:
-    __bootloader = grub
-else:
-    late = LatePolicyLoader()
-    if late.probe() == True:
-        __bootloader = late
+def init():
+    global __bootloader
+    grub = Grub()
+    if grub.probe() == True:
+        __bootloader = grub
+    else:
+        late = LatePolicyLoader()
+        if late.probe() == True:
+            __bootloader = late