Ignore failure to delete kernel/ramdisk in xenapi driver

Fixes bug 1022681

If deleting the kernel/ramdisk fails because the files don't exist
anymore, then ignore the error and continue. This will ensure that the
instance will get destroyed properly even if the files were deleted
outside of nova.

Change-Id: I5d1f95ea2a6f552c48efbb9e92bb36767df19e34

plugins/xenserver/xenapi/etc/xapi.d/plugins/kernel

@@ -20,6 +20,7 @@
 
 """Handle the manipulation of kernel images."""
 
+import errno
 import os
 import shutil
 
@@ -106,14 +107,22 @@ def create_kernel_ramdisk(session, args):
     return filename
 
 
+def _remove_file(filepath):
+    try:
+        os.remove(filepath)
+    except OSError, exc:
+        if exc.errno != errno.ENOENT:
+            raise
+
+
 def remove_kernel_ramdisk(session, args):
     """Removes kernel and/or ramdisk from dom0's file system"""
     kernel_file = optional(args, 'kernel-file')
     ramdisk_file = optional(args, 'ramdisk-file')
     if kernel_file:
-        os.remove(kernel_file)
+        _remove_file(kernel_file)
     if ramdisk_file:
-        os.remove(ramdisk_file)
+        _remove_file(ramdisk_file)
     return "ok"