Add schema attributes to root tag in DNS definition

Refs #11463

Code/Mantid/instrument/DNS_Definition_PAonly.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- For help on the notation used to specify an Instrument Definition File see http://www.mantidproject.org/IDF -->
-<instrument name="DNS" valid-from="1900-01-31 23:59:59" valid-to="2100-01-31 23:59:59" last-modified="2015-03-25 10:17:17">
+<instrument xmlns="http://www.mantidproject.org/IDF/1.0"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://www.mantidproject.org/IDF/1.0 http://schema.mantidproject.org/IDF/1.0/IDFSchema.xsd"
+	    name="DNS" valid-from="1900-01-31 23:59:59" valid-to="2100-01-31 23:59:59" last-modified="2015-03-25 10:17:17">
   <!-- Author: m.ganeva@fz-juelich.de -->
   <defaults>
     <length unit="meter" />