Test 573: Use correct type for CURLINFO_CONNECT_TIME

curl_easy_getinfo() called with a pointer to long instead of double
would sigbus on RISC processors (e.g. MIPS) due to wrong alignment
of pointer address.
diff --git a/tests/libtest/lib573.c b/tests/libtest/lib573.c
index e08b6df..db5889e 100644
--- a/tests/libtest/lib573.c
+++ b/tests/libtest/lib573.c
@@ -25,7 +25,7 @@
   CURLM *m = NULL;
   int res = 0;
   int running=1;
-  long connect_time = 0;
+  double connect_time = 0.0;
   struct timeval mp_start;
   char mp_timedout = FALSE;
 
@@ -83,8 +83,8 @@
   }
 
   curl_easy_getinfo(c, CURLINFO_CONNECT_TIME, &connect_time);
-  if (connect_time==0) {
-    fprintf(stderr, "connect time is 0\n");
+  if (connect_time==0.0) {
+    fprintf(stderr, "connect time is 0.0\n");
     res = TEST_ERR_MAJOR_BAD;
   }