Add minimal HTTP GET test

The test does a request and prints the responses. It is done to see that
the functionality works. Also added a timeout of 10 seconds to both the
connection and data transfer phases.

server/core/test/test_utils.cc

@@ -170,10 +170,25 @@ int test_checksums()
     return 0;
 }
 
+void test_http()
+{
+    auto res = mxs::http::get("https://mariadb.com/");
+    std::cout << "https://mariadb.com/ responded with: " << res.code << std::endl;
+    if (res.code == 200)
+    {
+        if (res.headers.count("Date"))
+        {
+            std::cout << "The date is: " << res.headers["Date"] << std::endl;
+        }
+    }
+}
+
 int main(int argc, char* argv[])
 {
     int rv = 0;
 
+    test_http(); // Just to see that it works
+
     rv += test_trim();
     rv += test_trim_leading();
     rv += test_trim_trailing();