Refactor use of JSON builder in tailExecutionOutput
Remove unsupported lock
Update core commons-lang, commons-beanutils deps

* match versions used by grails app
* commons-beanutils 1.8.3
* commons-lang-2.6
Fix timing issue: lastmodified for tailExecutionOutput

* if lastmodified was used, but no output was returned, don't change the
* client's last modified request value
Allow nullable for validated ExecutionQuery fields
Use framework server URL for api tests by default
Add sleep to prevent mtime timing issue for resource test
Improve debug output for errors