HttpServeShellCmdtHandler and http server changes

Adding HttpServeShellCmdtHandler to handle  Distributed Shell Command
Moving CommandUtility from reef-websever to helloHttp to share it with
ShellTask
HelloDriver to have all the event handlers
Remove helloTask
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
DriverServiceCOnfiguration
Move command utility to common
Use DriverServiceConfiguration
Update HttpServer/JettyHandler
Refactor adn clean up
Merged from master
merge from master
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
Update for review comments
use URLDecoder to decode the request string
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
RequestParser update
Update query string parser
minor refactoring in RequestParser: rename it into ParsedHttpRequest;
reformat the code, add finals and do minor optimizations
Add final for some variables in RequestParser
added one unit test for TestParsedHttpRequest
TestParsedHttpRequest unit test passes
add testHeaders() unit test; created setUp() section