MXS-3010: Fix maxkeys and the test

The test doesn't work properly if the maxscale user doesn't exist and the
key file permissions cannot be given to it. The test should use the
current user as the owner of the file but it turned out that the -u option
is broken.

Extended the test case to make sure the same password with the same
encryption key results in the same hash.

server/core/maxkeys.cc

@@ -62,9 +62,9 @@ int main(int argc, char** argv)
 
     int c;
 #ifdef HAVE_GLIBC
-    while ((c = getopt_long(argc, argv, "h", options, NULL)) != -1)
+    while ((c = getopt_long(argc, argv, "hu:", options, NULL)) != -1)
 #else
-    while ((c = getopt(argc, argv, "h")) != -1)
+    while ((c = getopt(argc, argv, "hu:")) != -1)
 #endif
     {
         switch (c)