xend: Fix error message for xm trigger command.

When I tested xm trigger command with a wrong argument, I saw the
following error message.

 # xm trigger vm1 xyz
 Error: __init__() takes exactly 2 arguments (3 given)
 Usage: xm trigger <Domain> <nmi|reset|init> [<VCPU>]

 Send a trigger to a domain.

This patch fixes the error message as follows.

 # xm trigger vm1 xyz
 Error: Invalid trigger: xyz
 Usage: xm trigger <Domain> <nmi|reset|init> [<VCPU>]

 Send a trigger to a domain.

The type of "TRIGGER_TYPE" is dictionary.  domain_send_trigger()
refers to the keys of "TRIGGER_TYPE" without using keys() currently.
This patch adds keys() there.

Signed-off-by: Masaki Kanno <kanno.masaki@jp.fujitsu.com>

tools/python/xen/xend/XendDomain.py

@@ -1594,10 +1594,10 @@ class XendDomain:
             raise VMBadState("Domain '%s' is not started" % domid,
                              POWER_STATE_NAMES[DOM_STATE_RUNNING],
                              POWER_STATE_NAMES[dominfo._stateGet()])
-        if trigger_name.lower() in TRIGGER_TYPE: 
+        if trigger_name.lower() in TRIGGER_TYPE.keys(): 
             trigger = TRIGGER_TYPE[trigger_name.lower()]
         else:
-            raise XendError("Invalid trigger: %s", trigger_name)
+            raise XendError("Invalid trigger: %s" % trigger_name)
         try:
             return xc.domain_send_trigger(dominfo.getDomid(),
                                           trigger,