Support our own apache access/error log names

It looks like the apache cookbook does not set a default access_log
attribute. Even if it did, it would probably be too generic for anyone
wanting to isolate access logs for openstack-dashboard. Similarly,
So, move this attribute into our own namespace and set the default as
"openstack-dashboard-access.log". As error logs fall into the same
dilemna, maintain consistency by also configuring their naming inside
this cookbook.

Change-Id: Iaa7c4202a14c6e3a963cb1bc5f37239c847264b0
Merge "Support our own apache access/error log names"