[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
Merge pull request #828 from haoxli/haoxli/usecase/webapi-nfc

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