When defining the mysql::db as exported resources, there are chances that the
same resource names are defined across the site, which will cause puppet agent
fail. By adding an optional dbname parameter, default to the $name, it allows the
resouce name to be defined differently, e.g. ${dbname}_${domain}.
Also updated test and docs for dbname parameter and add acceptance test for
dbname parameter feature
These tests are more or less parity with the rspec-system tests, though
dependent on a few patches that still have to make it into beaker and
beaker-rspec
