Allow CustomLog format string with space.

Avoid this error:
CustomLog takes two or three arguments, a file name, a custom log format string or format name, and an optional "env=" clause (see docs)
Quote CustomLog as in puppetlabs module
The vhost.erb is used in vhost/ssl.pp too

We need to duplicate the code here.
Merge pull request #109 from mremy/allow_space_in_customlog

Allow CustomLog format string with space.