Add find method in instance

Add find method in instance

Add a find method to get instances
based on rbname, version and profile.
If only rbname is provided, all instances based on
that resource bundle are returned.
If only rbname and version are provided, all instances
based on that combination are returned.
When all three parameters are provided, a single instance
that matches them is returned.

Issue-ID: MULTICLOUD-613
Change-Id: If63e844c77829211b807ce6cd7c11dad247751fc
Signed-off-by: Kiran Kamineni <kiran.k.kamineni@intel.com>