force our exit trap to always run (for rtnstate commands) (#556)

* add command validation to shellapi.  mock out bash/zsh versions

* implement validate command fn bash and zsh

* test validate command

* change rtnstate commands to always end with a builtin, so we always get our exit trap to run

* simplify the rtnstate modification, don't add the 'wait' (as this is a different problem/feature)

* update schema

wavesrv/pkg/remote/remote.go

@@ -1735,7 +1735,7 @@ func (msh *MShellProc) Launch(interactive bool) {
 	msh.WriteToPtyBuffer("connected to %s\n", remoteCopy.RemoteCanonicalName)
 	go func() {
 		exitErr := cproc.Cmd.Wait()
-		exitCode := shexec.GetExitCode(exitErr)
+		exitCode := utilfn.GetExitCode(exitErr)
 		msh.WithLock(func() {
 			if msh.Status == StatusConnected || msh.Status == StatusConnecting {
 				msh.Status = StatusDisconnected