Fix empty Database-names in dbi-plugin
Fix empty Database-names in dbi-plugin

Right now, this pseudo Puppet-code:

	::collectd::plugin::dbi::query { 'test': ... }
	::collectd::plugin::dbi::database { 'test':
		driver => 'mysql',
		driveroption => {
			'host' => 'localhost',
			'mysql_unix_socket' => ...,
			'username' => ...,
			'password' => ...,
			'dbname' => ...,
		},
		query => [ 'test' ],
	}

produces these configuration blocks:

	<Plugin dbi>
		<Query test>
			...
		</Query>
		<Database "">       <-----
			...
		</Database>
	</Plugin>

The database-name references a non-existent @databasename variable, so introduce
this variable, as it is also introduced and used inside
::collectd::postgresql::database, so that the expected output is produced:

	<Plugin dbi>
		<Query test>
			...
		</Query>
		<Database "test">   <-----
			...
		</Database>
	</Plugin>

archii/puppet-collectd,voxpupuli/puppet-collectd,juniorsysadmin/puppet-collectd,voxpupuli/puppet-collectd,archii/puppet-collectd,voxpupuli/puppet-collectd,juniorsysadmin/puppet-collectd,archii/puppet-collectd