tests: use %LOGDIR to refer to the log directory

This will allow it be set dynamically.

Ref: #10818

tests/data/test1376

@@ -30,10 +30,10 @@ http
 HTTP GET -o fname -i without Content-Disposition, without -D
 </name>
 <command option="no-output,no-include">
-http://%HOSTIP:%HTTPPORT/%TESTNUMBER -i -o log/outfile%TESTNUMBER
+http://%HOSTIP:%HTTPPORT/%TESTNUMBER -i -o %LOGDIR/outfile%TESTNUMBER
 </command>
 <postcheck>
-perl %SRCDIR/libtest/notexists.pl log/%TESTNUMBER
+perl %SRCDIR/libtest/notexists.pl %LOGDIR/%TESTNUMBER
 </postcheck>
 </client>
 
@@ -48,7 +48,7 @@ Accept: */*
 
 </protocol>
 
-<file1 name="log/outfile%TESTNUMBER">
+<file1 name="%LOGDIR/outfile%TESTNUMBER">
 HTTP/1.1 200 OK
 Date: Tue, 09 Nov 2010 14:49:00 GMT
 Server: test-server/fake
@@ -59,7 +59,7 @@ Content-Type: text/html
 12345
 </file1>
 
-<file2 name="log/stdout%TESTNUMBER">
+<file2 name="%LOGDIR/stdout%TESTNUMBER">
 </file2>
 
 </verify>