[uecase-webapi][XWALK-2251] Improve nfc usecase

 - Change status to approved
 - Add clearLog function and setEnvironment function
 - Removed redundant test functions
 - Modified AddMessage function
 - Improve test steps and excepted results

 - Failure analysis: 1. startPoll() method does not work, can not change nfc hardware to polling mode, then nfc tag and peer device can not found.
                             2. When ran NFCTag::readNDEF(), NFCTag::writeNDEF(), NFCPeer::sendNDEF() method, neither callback was invoked.

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: pass 0, fail 1, block 0