Cleanup in LanItemsClass#GetDeviceName
Removed useless code
Exclude tun from bridgeble interfaces.

tun device is not supported as a bridge port
Fixed testsuite
IsBridgeable: cleanup
ValidateBridge: cleanup
ValidateBridge: simplifying the code
Changes according bnc#879617
Updated testsuite: cover LanItemsClass#FindAndSelect
Refactored LanItemsClass#FindAndSelect
Splitted bridge port configuration updating code
Modified updating configuration ValidateBridge according bnc#879617
Removed useless code
Added comment
Moved storing bridge ports configuration out of validation handler.
ValidateBridge: another cleanup
InitBridge: cleanup
Updated changelog