Fix retrieving operations resource

Fix retrieving operations resource

Fix retrieving operations resource from controller and mount points
by adapting getOperationsJSON/XML to accept identifiers and enhancing
its functionality with ability to match exact operation.

This way we enhance solution proposed by NETCONF-822 to cover
all use cases and avoid error 500.

JIRA: NETCONF-928
JIRA: NETCONF-929
Change-Id: Ic8f0ca5b07e060d36747a110f9049d3d9a2b96c8
Signed-off-by: Yaroslav Lastivka <yaroslav.lastivka@pantheon.tech>
Signed-off-by: Ivan Hrasko <ivan.hrasko@pantheon.tech>
Signed-off-by: Peter Suna <peter.suna@pantheon.tech>