tst_QPrinter: stabilize qprinter test

The CreationDate entry in the two PDF files can potentially
be different depending on when the test is run.
97b4c5a574 already accounts for it but
the current tag for creation date is '/CreationDate'. Therefore check
if the line contains 'CreationDate' instead.

Change-Id: I1fc069cf935bba07084ac4a0743ff05312374d10
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/printsupport/kernel/qprinter/tst_qprinter.cpp

@@ -644,7 +644,7 @@ void tst_QPrinter::taskQTBUG4497_reusePrinterOnDifferentFiles()
         QByteArray file1Line = file1.readLine();
         QByteArray file2Line = file2.readLine();
 
-        if (!file1Line.startsWith("%%CreationDate"))
+        if (!file1Line.contains("CreationDate"))
             QCOMPARE(file1Line, file2Line);
     }