Update config loader to throw a more user-friendly exception if rendering a particular dynamic config value fails.
Update config loader to throw a more user-friendly exception if rendering a
particular dynamic config value fails.

lakshmi-kannan/st2,peak6/st2,StackStorm/st2,nzlosh/st2,tonybaloney/st2,lakshmi-kannan/st2,tonybaloney/st2,peak6/st2,StackStorm/st2,peak6/st2,nzlosh/st2,Plexxi/st2,tonybaloney/st2,Plexxi/st2,nzlosh/st2,Plexxi/st2,lakshmi-kannan/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,StackStorm/st2