fix one spelling mistake and two help messages

I checked all the 70 rst files in doc/source/command-objects and
found that:
 -one spelling mistake as:rescure should be rescue(server.rst)
 -two help messages:xpvnc should be xvpvnc(console-url.rst and
  console.py)

Change-Id: I6f46c79983eaf5650bd3aa0ab448c19f5c6527a9

Author: zhengsenyan

doc/source/command-objects/console-url.rst

@@ -24,7 +24,7 @@ Show server's remote console URL
 
 .. option:: --xvpvnc
 
-    Show xpvnc console URL
+    Show xvpvnc console URL
 
 .. option:: --spice
 

doc/source/command-objects/server.rst

@@ -543,7 +543,7 @@ server rescue
 
 Put server in rescue mode
 
-.. program:: server rescure
+.. program:: server rescue
 .. code:: bash
 
     os server rescue

openstackclient/compute/v2/console.py

@@ -87,7 +87,7 @@ def get_parser(self, prog_name):
             dest='url_type',
             action='store_const',
             const='xvpvnc',
-            help=_("Show xpvnc console URL")
+            help=_("Show xvpvnc console URL")
         )
         type_group.add_argument(
             '--spice',