[Android] Correct the error message for embedded sample app

Change to more general term:
"Crosswalk failed to initialize."
The detail information about the failure will be shown in
the pop up dialog.

BUG=https://crosswalk-project.org/jira/browse/XWALK-649
Merge pull request #1306 from wang16/runtime_warn

[Android] Correct the error message for embedded sample app