Correct regexp warning in vhost_spec.rb

Without this patch, running the spec tests encounter a warning
about a regular expresion with a '}' that has not been escaped. This
warning is from line 238 in the vhost_spec.rb file.

This commit eliminates that warning.
Merge pull request #183 from trlinkin/master

Remove spec test warning
Merge pull request #184 from trlinkin/refactor_vhost_logformat

Refactor vhost logformat
Add Validation and rspec tests for $error_log

Without this commit, there is no validation or testing for the
$error_log parameter in the apache::vhost type.

This commit add boolean validation to the apache::vhost type. It also
adds two rspec tests to test the proper function of the parameter.