Refactor OLM PowerMgmtImpl class

Refactor OLM PowerMgmtImpl class

The former implementation of OLM Power management ignored some spotbugs
warnings and triggered many alarms in SonarCloud, mainly about
commented-out lines of code and the SetPower method.
This method had 280 lines and its cyclomatic complexity was 43.
Current Sonar rules warns methods with more than 75 lines of code
and a cyclomatic complexity of 10.

As a consequence
- remove commented-out lines of code
- fix SpotBugs warnings and remove annotations to ignore them
- split the SetPower method into several pieces
- rework and optimize the code
- add TODO and FIXME comments for some parts of the code
  that may need to be reconsidered in the future

JIRA: TRNSPRTPCE-211 TRNSPRTPCE-494
Signed-off-by: guillaume.lambert <guillaume.lambert@orange.com>
Change-Id: Iae5644f66cd6de6e17f81de3cd61dcb546ac2dd1