This implements a special "RESET" value that can be used to reset the
list of capabilities to add/drop when updating a service.
Given the following service;
| CapDrop | CapAdd |
| -------------- | ------------- |
| CAP_SOME_CAP | |
When updating the service, and applying `--cap-drop RESET`, the "drop" list
is reset to its default:
| CapDrop | CapAdd |
| -------------- | ------------- |
| | |
When updating the service, and applying `--cap-drop RESET`, combined with
`--cap-add CAP_SOME_CAP` and `--cap-drop CAP_SOME_OTHER_CAP`:
| CapDrop | CapAdd |
| -------------- | ------------- |
| CAP_FOO_CAP | CAP_SOME_CAP |
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>