[PATCH branch-2.1] Fix error output in LUSetClusterParams

[Iustin Pop]

Before:
  gnt-cluster modify --enabled-hypervisors=xen-hvm,xem-pvm
  Failure: command execution error:
  Enabled hypervisors contains invalid entries: set([u'xem-pvm'])

After:
  gnt-cluster modify --enabled-hypervisors=xen-hvm,xem-pvm
  Failure: command execution error:
  Enabled hypervisors contains invalid entries: 'xem-pvm'
---
 lib/cmdlib.py |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/lib/cmdlib.py b/lib/cmdlib.py
index 93f9e4f..02a5128 100644
--- a/lib/cmdlib.py
+++ b/lib/cmdlib.py
@@ -1820,7 +1820,8 @@ class LUSetClusterParams(LogicalUnit):
       invalid_hvs = set(self.hv_list) - constants.HYPER_TYPES
       if invalid_hvs:
         raise errors.OpPrereqError("Enabled hypervisors contains invalid"
-                                   " entries: %s" % invalid_hvs)
+                                   " entries: %s" %
+                                   utils.CommaJoin(invalid_hvs))
     else:
       self.hv_list = cluster.enabled_hypervisors
 
-- 
1.6.3.3