Klr should gracefully exit if run on a folder without a project.json

[Praburaj]

Today when k is being run on a folder where there is no project.json klr crashes with this exception. Instead we should print the message and gracefully shutdown klr.exe.

Unhandled Exception: System.AggregateException: One or more errors occurred. ---
> System.Exception: Unable to locate project.json
   at Microsoft.Framework.Runtime.DefaultHost.Initialize(DefaultHostOptions opti
ons)
   at Microsoft.Framework.Runtime.DefaultHost..ctor(DefaultHostOptions options,
IServiceProvider hostProvider)
   at Microsoft.Framework.ApplicationHost.Program.<Main>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNot
ification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.Framework.Runtime.Common.EntryPointExecutor.<Execute>d__1.MoveNe
xt()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNot
ification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at klr.host.Bootstrapper.<Main>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNot
ification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at klr.hosting.RuntimeBootstrapper.<Execute>d__1.MoveNext()
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotifica
tion)
   at System.Threading.Tasks.Task`1.get_Result()
   at DomainManager.Execute(Int32 argc, Char** argv)

[davidfowl]

Dupe of #119