Implement worker removal from the pool

Implement worker removal from the pool

When Worker will not be used anymore, it should be removed in order
to free the resources. Administrator should first put Worker
in the MAINTENANCE state, using SetState, and then remove it,
using Deregister.

Change-Id: Ic9bb5e705418fae664857f3f541e9543ca7da9e2
Signed-off-by: Aleksander Mistewicz <a.mistewicz@samsung.com>
Reviewed-on: https://mcdsrvbld02.digital.local/review/49058
Reviewed-by: Maciej Wereski <m.wereski@partner.samsung.com>
Tested-by: Maciej Wereski <m.wereski@partner.samsung.com>