FRM to expose list of installed flow entries per group

FRM to expose list of installed flow entries per group

    ISSUE:
    Given a group/policy name, ForwardingRulesManager only provides a function to return the list of Flow Entry it was requested to install.
    In presence of container flows, this list does not represent the actual entries which were installed on the network nodes for that group.
    CHANGE:
    Add getInstalledFlowEntriesForGroup(String policyName) to IForwardingRulesManager.

Change-Id: Ie26d64c05d5eb49b3073d34d701ea1fa5b05adfa
Signed-off-by: Alessandro Boch <aboch@cisco.com>