Normalize some php.ini configuration in daemon scripts

Summary: Users may set 'error_log' to something other than the default, which
confusingly writes error data somewhere other than the console when running
exec_daemon.php or "phd debug". Force error-related configuration to the values
we expect.

Test Plan: Applied patch on a box with 'error_log' set to 'error_log', got
useful information on stderr and information propagation via "phd debug".

Reviewers: btrahan, jungejason

Reviewed By: jungejason

CC: aran, jungejason

Differential Revision: https://secure.phabricator.com/D1402