[embedding][XWALK-895] Add new embedding api tests for xwalk

Impacted Suites:webapi-embeddingapi-xwalk-tests
Impated TCs num:New 17, Update 0, Delete 0
Unit test platform: android
Android Test result summary:pass 14,Fail 3,Blocked 0
This method(getInstance()) and this attribute(instance) is not used， I will remove.