For Server instances without a check-alive URL, perform a default check-alive

[halfer]

A Server without a check-alive will try to run tests before the server has had chance to stabilise:

php vendor/bin/phpunit 
PHPUnit 6.1.0 by Sebastian Bergmann and contributors.

E                                                                   1 / 1 (100%)

Time: 87 ms, Memory: 2.00MB

There was 1 error:

1) halfer\SpiderlingUtils\NamespaceDemo\SimpleTest::testAnything
Openbuildings\Spiderling\Exception_Curl: Curl: Download Error: Failed to connect to localhost port 8090: Connection refused, status 0 on url http://localhost:8090/

.../vendor/openbuildings/spiderling/src/Openbuildings/Spiderling/Driver/Simple/RequestFactory/HTTP.php:87
.../vendor/openbuildings/spiderling/src/Openbuildings/Spiderling/Driver/Simple.php:227
.../vendor/openbuildings/spiderling/src/Openbuildings/Spiderling/Driver/Simple.php:182
.../vendor/openbuildings/spiderling/src/Openbuildings/Spiderling/Driver/Simple.php:420
.../vendor/openbuildings/spiderling/src/Openbuildings/Spiderling/Page.php:33
.../vendor/openbuildings/phpunit-spiderling/src/TestCase.php:181
.../test/SimpleTest.php:14

ERRORS!
Tests: 1, Assertions: 0, Errors: 1.

As a result of this crash, the code to clean up the forked server does not run, and it persists until manually killed.

A default check-alive should be added to this, unless it is explicitly turned off.