Fix : logic error in MDM visibility policy

Fix : logic error in MDM visibility policy

[Problem] There are some logic error regarding Discoverable property
 changed event.
1. When limited discoverable mode is not allowed and general
discoverable is set, general discoverable is requested again.
2. When limited discoverable mode and discoverable mode are both not
allowed, it tries to set general discoverable mode.
3. DiscoverableTimeout property is not updated.
[Cause & Measure] 1. Check current discoverable mode and only if it is
in limited discoverable mode and limited discoverable mode is not
allowed, set to general discoverable mode.
2. After handling discoverable mode policy, don't check limited
discoverable mode policy.
3. Use proper type to set DiscoverableTimeout property.
[Checking Method] Code review

Change-Id: I3246ab7019c5415e799e448ce4115103211f4e6c