Implement get information about the Worker

Implement get information about the Worker

In order to avoid listing workers when information about only one is
needed, a convenience function has been added. It is faster and
guarantees that a single structure will be returned or an error.

workers/workers_test.go has been removed as all functions has been
implemented.

Change-Id: I0dfaccc4c55bdb30c5875de06db9d3b23b2345b2
Signed-off-by: Aleksander Mistewicz <a.mistewicz@samsung.com>
Reviewed-on: https://mcdsrvbld02.digital.local/review/49062
Reviewed-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Tested-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Reviewed-by: Maciej Wereski <m.wereski@partner.samsung.com>
Tested-by: Maciej Wereski <m.wereski@partner.samsung.com>