tests: use %TESTNUMBER instead of fixed number

This makes the tests easier to copy and relocate to other test numbers
without having to update content.

Closes #6738

tests/data/test573

@@ -32,21 +32,21 @@ http
 </server>
 # tool is what to use instead of 'curl'
 <tool>
-lib573
+lib%TESTNUMBER
 </tool>
 
  <name>
 verify connect time with multi interface
  </name>
  <command>
-http://%HOSTIP:%HTTPPORT/573
+http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 </command>
 </client>
 
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
-GET /573 HTTP/1.1
+GET /%TESTNUMBER HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
 Accept: */*