Support get roles call with optional Service Id param.

Fix proposed to branch: master
Review: https://review.openstack.org/2560

This is how the list roles method is defined in the wadl
Ref: https://github.com/openstack/keystone/blob/master/keystone/content/admin/OS-KSADM-admin.wadl

<!--Roles-->
<method name="GET" id="listRoles">
<doc xml:lang="EN" title="List Roles">
<p xmlns="http://www.w3.org/1999/xhtml">List roles.</p>

</doc>
<request>
<param name="serviceId" style="query" required="false" type="xsd:string"/> => Optional service id
<param name="marker" style="query" required="false" type="xsd:string"/>
<param name="limit" style="query" required="false" type="xsd:int"/>
</request>
<response status="200 203">
<representation mediaType="application/xml" element="identity:roles">
<doc xml:lang="EN">
<xsdxt:code href="../common/samples/roles.xml"/>
</doc>
</representation>
<representation mediaType="application/json">
<doc xml:lang="EN">
<xsdxt:code href="../common/samples/roles.json"/>
</doc>
</representation>
</response>
&commonFaults;
&getFaults;
</method>

Our list roles method should support the same call with an optional serviceId as our wadl supports the optional call with serviceId.

Reviewed: https://review.openstack.org/2560
Committed: http://github.com/openstack/keystone/commit/620d2ff33d8f4994d0f31b6c04c38910ce63a082
Submitter: Jenkins
Branch: master

commit 620d2ff33d8f4994d0f31b6c04c38910ce63a082
Author: Yogeshwar Srikrishnan <email address hidden>
Date: Thu Dec 22 09:54:21 2011 -0600

     Bug #907521.
        Changes to support get roles by service.

    Change-Id: I0646ab91f6961e5e3ed40b8697412c31047511d3