Enforce all error report for php tests. (#3670)

* Enforce all error report for php tests.

* Import vendor/autoload.php in tests/bootstrap_phpunit.php
diff --git a/php/phpunit.xml b/php/phpunit.xml
index d707703..87440bb 100644
--- a/php/phpunit.xml
+++ b/php/phpunit.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit bootstrap="./vendor/autoload.php"
+<phpunit bootstrap="./tests/bootstrap_phpunit.php"
          colors="true">
   <testsuites>
     <testsuite name="protobuf-tests">