Improve apache_error format

Hi @repeatedly

This PR supports apache error log format without host key.
c.f. https://gist.github.com/y-ken/a542b466c5998d03d148

These pattern are supported by this PR.

```
2014-08-19 17:44:22 +0900 [warn]: pattern not match: "[Tue Aug 05 15:48:43 2014] [notice] Apache/2.2.15 (Unix) DAV/2 configured -- resuming normal operations"
2014-08-19 17:44:22 +0900 [warn]: pattern not match: "[Thr Mar 29 17:52:01 2007] [notice] child pid 20001 exit signal Segmentation fault (11)"
```