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/test643

@@ -44,14 +44,14 @@ http
 </server>
 # tool is what to use instead of 'curl'
 <tool>
-lib643
+lib%TESTNUMBER
 </tool>
 
  <name>
 HTTP multi-part mimepost using read callback for the file part
  </name>
  <command>
-http://%HOSTIP:%HTTPPORT/643
+http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 </command>
 </client>
 
@@ -66,7 +66,7 @@ s/boundary=------------------------[a-z0-9]*/boundary=--------------------------
 # boundary string and since 5 of them are in the body contents, we see
 # (5*12) == 60 bytes less
 <protocol>
-POST /643 HTTP/1.1
+POST /%TESTNUMBER HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
 Accept: */*
 Content-Length: 640
@@ -96,7 +96,7 @@ Content-Type: text/plain
 
 blah blah
 --------------------------------
-POST /643 HTTP/1.1
+POST /%TESTNUMBER HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
 Accept: */*
 Content-Length: 654