[COOK-4617] Added service name attribute.

CLA: Signed (waiting for Developer status in Jira, so I can mark it as 'Fix Provided')
Ticket: https://tickets.opscode.com/browse/COOK-4617

Add a service name attribute, so it can be re-used in other cookbooks that depend on tomcat cookbook.

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For example, the `application_java` cookbook uses hardcoded `tomcat` service name currently:
https://github.com/poise/application_java/blob/master/providers/tomcat.rb#L48

In the future it may use this attribute, because it already depends on tomcat cookbook.