Install phpdbg (#1612)

* Install phpdbg
* Change documentstion

env-example

@@ -87,6 +87,7 @@ WORKSPACE_INSTALL_PHPREDIS=true
 WORKSPACE_INSTALL_WORKSPACE_SSH=false
 WORKSPACE_INSTALL_SUBVERSION=false
 WORKSPACE_INSTALL_XDEBUG=false
+WORKSPACE_INSTALL_PHPDBG=false
 WORKSPACE_INSTALL_LDAP=false
 WORKSPACE_INSTALL_SOAP=false
 WORKSPACE_INSTALL_IMAP=false
@@ -132,6 +133,7 @@ PHP_FPM_INSTALL_IMAGE_OPTIMIZERS=true
 PHP_FPM_INSTALL_PHPREDIS=true
 PHP_FPM_INSTALL_MEMCACHED=false
 PHP_FPM_INSTALL_XDEBUG=false
+PHP_FPM_INSTALL_PHPDBG=false
 PHP_FPM_INSTALL_IMAP=false
 PHP_FPM_INSTALL_MONGO=false
 PHP_FPM_INSTALL_AMQP=false