Allow use different name for db resource other than db name

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
Use ensure_resource for mysql_databasein mysql::db

This will allow exported resource mysql::db to define same database but different
hostname and enables the cluster web nodes to declear the mysql::db and
to be collected on db node.
Merge pull request #489 from xcompass/exported-resource-mysql-db

Allow to use different name for db resource other than db name
Fixed travis by updating Gemfile to pin Rake to 10.1.1

The latest Rake update requires Ruby >= 1.9. This update
fixes the failing 1.8.7 tests by pinning Rake to the last
supported version on ruby 1.8.7.

This is a direct copy from @blkperl's fix for puppetlabs-apache
https://github.com/puppetlabs/puppetlabs-apache/pull/685
Merge pull request #493 from igalic/rake

Fixed travis by updating Gemfile to pin Rake to 10.1.1