Make make_webapp.py more flexible

The name of build tool has changed from v3.32.51.0 in 01.org
This PR fixes this issue, and it can support all the versions of build tool.

BUG=https://crosswalk-project.org/jira/browse/XWALK-661
Merge pull request #47 from kurli/version-fix

Make make_webapp.py more flexible