Return valid code from test fixture on failure.

The sshd test fixture was returning -1 if an error occurred, but negative error codes aren't technically valid (google it).  Bash on Windows converted them to 0 which made setup failure look as though all tests were passing.

tests/ssh2.c

@@ -80,7 +80,7 @@ int main(int argc, char *argv[])
     if (connect(sock, (struct sockaddr*)(&sin),
                 sizeof(struct sockaddr_in)) != 0) {
         fprintf(stderr, "failed to connect!\n");
-        return -1;
+        return 1;
     }
 
     /* Create a session instance and start it up
@@ -89,7 +89,7 @@ int main(int argc, char *argv[])
     session = libssh2_session_init();
     if (libssh2_session_startup(session, sock)) {
         fprintf(stderr, "Failure establishing SSH session\n");
-        return -1;
+        return 1;
     }
 
     /* At this point we havn't authenticated,