Use the actual bool type instead of a fake enum

Use the actual bool type instead of a fake enum

Improves type correctness and fixes a case of two functions
being identical - `log_config_get_boolean` used to just call
`log_config_get_int` with the same parameters and did not
even touch the return value.

Includes tests for `log_config_get_boolean`.

Change-Id: I185dfac32d40bcab3ddbf95d3b4536c2d275098e
Signed-off-by: Michal Bloch <m.bloch@samsung.com>