Add separate UsePty flag for CmdObj

This decouples StreamOutput from whether a PTY is used. In most cases we just
want to see the output in the log window, but don't have to use a PTY, e.g. for
the bisect commands.

This has the implication that custom commands that are using "stream: true" no
longer use a PTY. In most cases that's probably a good thing, but we're going to
add a separate pty config for those who really wanted this.

pkg/commands/oscommands/cmd_obj_runner.go

@@ -238,7 +238,13 @@ func (self *cmdObjRunner) runAndStreamAux(
 	var stderr bytes.Buffer
 	cmd.Stderr = io.MultiWriter(cmdWriter, &stderr)
 
-	handler, err := self.getCmdHandlerPty(cmd)
+	var handler *cmdHandler
+	var err error
+	if cmdObj.ShouldUsePty() {
+		handler, err = self.getCmdHandlerPty(cmd)
+	} else {
+		handler, err = self.getCmdHandlerNonPty(cmd)
+	}
 	if err != nil {
 		return err
 	}