Fix typos for stack.sh and lib of comments and message

Fix 10 comments and 1 message

stack.sh
  Certicate => Certificate (comment)
lib/stack
  Sentinal => Sentinel (comment)
lib/neutron-legacy
  overriden => overridden (comment)
  necesssary => necessary (comment)
  notifiy => notify (message)
  notifations => notifications (comment)
lib/rpc_backend
  orginal => original (comment)
  cofiguration => configuration (comment)
lib/stack
  confgured => configured (comment)
lib/swift
  additinal => additional (comment)
  calclution => calculation (comment)
  maximun => maximum (comment)

Change-Id: I3637388b67decb007cd49af9addecc654009559b
diff --git a/lib/stack b/lib/stack
index 47e8ce2..7d98604 100644
--- a/lib/stack
+++ b/lib/stack
@@ -14,7 +14,7 @@
 # Functions
 # ---------
 
-# Generic service install handles venv creation if confgured for service
+# Generic service install handles venv creation if configured for service
 # stack_install_service service
 function stack_install_service {
     local service=$1