schema: Allow lxc:namepsace children to appear individually

Since its introduction in v1.2.19-rc1~8 our schema mandates that
LXC domain namespace child elements appear either all three at
once or not at all:

     <lxc:namespace>
       <lxc:sharenet type='netns' value='red'/>
       <lxc:shareipc type='pid' value='12345'/>
       <lxc:shareuts type='name' value='container1'/>
     </lxc:namespace>

This is not mandated by our parser though. Neither by code that
later uses it (virLXCProcessSetupNamespaces()). Relax the schema.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>

docs/schemas/domaincommon.rng

@@ -6821,7 +6821,8 @@
     -->
   <define name="lxcsharens">
     <element name="namespace" ns="http://libvirt.org/schemas/domain/lxc/1.0">
-      <zeroOrMore>
+      <interleave>
+        <optional>
           <element name="sharenet">
             <attribute name="type">
               <choice>
@@ -6832,6 +6833,8 @@
             </attribute>
             <attribute name="value"/>
           </element>
+        </optional>
+        <optional>
           <element name="shareipc">
             <attribute name="type">
               <choice>
@@ -6841,6 +6844,8 @@
             </attribute>
             <attribute name="value"/>
           </element>
+        </optional>
+        <optional>
           <element name="shareuts">
             <attribute name="type">
               <choice>
@@ -6850,7 +6855,8 @@
             </attribute>
             <attribute name="value"/>
           </element>
-      </zeroOrMore>
+        </optional>
+      </interleave>
     </element>
   </define>