Change char* to enum in context->update & refactor code

Change char* to enum in context->update & refactor code

Storing update option in string is bad for frequent comparisons and
error prone.
Replace char array with enum so already existing enum is passed around
instead of string.
Adapt code to changes.

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