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/test514

@@ -30,14 +30,14 @@ Funny-head: yesyes
 http
 </server>
 <tool>
-lib514
+lib%TESTNUMBER
 </tool>
  <name>
 First set options to POST and then to make HEAD
  </name>
 # the 1s post-command delay helps to prevent a spurious failure on s390
  <command delay="1">
-http://%HOSTIP:%HTTPPORT/514
+http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 </command>
 </client>
 
@@ -45,7 +45,7 @@ http://%HOSTIP:%HTTPPORT/514
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
-HEAD /514 HTTP/1.1
+HEAD /%TESTNUMBER HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
 Accept: */*