Merge pull request #2402 from cs278/perforce-driver-fixes

Perforce driver fixes

src/Composer/Repository/Vcs/PerforceDriver.php

@@ -162,7 +162,7 @@ class PerforceDriver extends VcsDriver
     public static function supports(IOInterface $io, Config $config, $url, $deep = false)
     {
         if ($deep || preg_match('#\b(perforce|p4)\b#i', $url)) {
-            return Perforce::checkServerExists($url, new ProcessExecutor);
+            return Perforce::checkServerExists($url, new ProcessExecutor($io));
         }
 
         return false;

src/Composer/Util/Perforce.php

@@ -372,7 +372,9 @@ class Perforce
 
     public static function checkServerExists($url, ProcessExecutor $processExecutor)
     {
-        return 0 === $processExecutor->execute('p4 -p ' . $url . ' info -s');
+        $output = null;
+
+        return 0 === $processExecutor->execute('p4 -p ' . $url . ' info -s', $output);
     }
 
     public function getComposerInformation($identifier)