[embedding][XWALK-2381] Change loadAppFromManifest mode to sync and improve pack.sh and loadUrl

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Android]
Unit test result summary: pass 84, fail 18, block 4
Merge pull request #771 from zhuyongyong/yongzhu/embeddingAPI-tests/loadUrl

[embedding][XWALK-2381] Change loadAppFromManifest mode to sync and improve pack.sh