under Debian 8 package name for ruby mysql biding is called ruby-mysql, just like trusty.

Zouuup · Zouuup · commit 9f9061ea8fe8 · 2014-12-19T17:03:46.000+03:30
diff --git a/manifests/params.pp b/manifests/params.pp
@@ -167,6 +167,7 @@
       $python_package_name = 'python-mysqldb'
       $ruby_package_name   = $::lsbdistcodename ? {
         'trusty'           => 'ruby-mysql',
+        'jessie'           => 'ruby-mysql',        
         default            => 'libmysql-ruby',
       }
       $client_dev_package_name = 'libmysqlclient-dev'

Original file line number	Diff line number	Diff line change
`@@ -167,6 +167,7 @@`
`167`	`167`	`$python_package_name = 'python-mysqldb'`
`168`	`168`	`$ruby_package_name = $::lsbdistcodename ? {`
`169`	`169`	`'trusty' => 'ruby-mysql',`
	`170`	`+ 'jessie' => 'ruby-mysql',`
`170`	`171`	`default => 'libmysql-ruby',`
`171`	`172`	`}`
`172`	`173`	`$client_dev_package_name = 'libmysqlclient-dev'`