test1513: eliminated race condition in test run

It seems that some systems (e.g. fairly consistently in some recent
Solaris autobuilds) would manage to get to the connect phase before the
progress callback was called, resulting in a CURLE_COULDNT_CONNECT
error. Reworked the test to point at a test server that never returns a
full result so the progress callback always gets a chance to be called
before the transfer can complete in some other way.