Manage&Incremental: code refactor, string to enum

Manage&Incremental: code refactor, string to enum

Prepare Manage and Incremental for later changing context->update to enum.
Change update from string to enum in multiple functions and pass enum
where already possible.

Signed-off-by: Mateusz Kusiak <mateusz.kusiak@intel.com>
Signed-off-by: Jes Sorensen <jes@trained-monkey.org>