XenError dies if no XML file on the filesystem

[matelakat]

If the filesystem doesn't have the:
/opt/xensource/sm/XE_SR_ERRORCODES.xml
file, it fails in a very ugly way:

on xs64bit:

======================================================================
ERROR: test_mount (test_NFSSR.TestNFSSR)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/storage-manager/sm/tests/testlib.py", line 279, in decorated
    result = func(self, context, *args, **kwargs)
  File "/storage-manager/sm/tests/test_NFSSR.py", line 34, in test_mount
    sr = create_nfs_sr()
  File "/storage-manager/sm/tests/test_NFSSR.py", line 27, in create_nfs_sr
    sr = NFSSR.NFSSR(command, '0')
  File "/storage-manager/sm/drivers/SR.py", line 139, in __init__
    self.load(sr_uuid)
  File "/storage-manager/sm/drivers/NFSSR.py", line 75, in load
    raise xs_errors.XenError('ConfigServerMissing')
  File "/storage-manager/sm/drivers/xs_errors.py", line 32, in __init__
    raise Exception.__init__(self, '')
TypeError: TypeError: unbound method __init__() must be called with Exception instance as first argument (got XenError instance instead)

on trunk:

======================================================================
ERROR: test_mount (test_NFSSR.TestNFSSR)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/storage-manager/sm/tests/testlib.py", line 279, in decorated
    result = func(self, context, *args, **kwargs)
  File "/storage-manager/sm/tests/test_NFSSR.py", line 34, in test_mount
    sr = create_nfs_sr()
  File "/storage-manager/sm/tests/test_NFSSR.py", line 27, in create_nfs_sr
    sr = NFSSR.NFSSR(command, '0')
  File "/storage-manager/sm/drivers/SR.py", line 139, in __init__
    self.load(sr_uuid)
  File "/storage-manager/sm/drivers/NFSSR.py", line 75, in load
    raise xs_errors.XenError('ConfigServerMissing')
  File "/storage-manager/sm/drivers/xs_errors.py", line 32, in __init__
    raise Exception.__init__(self, '')
TypeError: TypeError: exceptions must be classes, instances, or strings (deprecated), not NoneType

So we should come up with a different fix, something like:

--- a/drivers/xs_errors.py
+++ b/drivers/xs_errors.py
@@ -28,8 +28,7 @@ class XenError(object):
     def __init__(self, key, opterr=None):
         # Check the XML definition file exists
         if not os.path.exists(XML_DEFS):
-            print "No XML def file found"
-            raise Exception.__init__(self, '')
+            raise Exception("No XML def file found")

         # Read the definition list
         self._fromxml('SM-errorcodes')

In this case you get the output:

======================================================================
ERROR: test_mount (test_NFSSR.TestNFSSR)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/storage-manager/sm/tests/testlib.py", line 279, in decorated
    result = func(self, context, *args, **kwargs)
  File "/storage-manager/sm/tests/test_NFSSR.py", line 34, in test_mount
    sr = create_nfs_sr()
  File "/storage-manager/sm/tests/test_NFSSR.py", line 27, in create_nfs_sr
    sr = NFSSR.NFSSR(command, '0')
  File "/storage-manager/sm/drivers/SR.py", line 139, in __init__
    self.load(sr_uuid)
  File "/storage-manager/sm/drivers/NFSSR.py", line 75, in load
    raise xs_errors.XenError('ConfigServerMissing')
  File "/storage-manager/sm/drivers/xs_errors.py", line 31, in __init__
    raise Exception("No XML def file found")
Exception: No XML def file found

Which now makes sense