Support global opts for ovs/ovn commands in batch mode

[hzhou8]

There are two kinds of opts for ovs/ovn command lines: global and command specific, as documented in man page of ovs-vsctl:
"The ovs-vsctl command line begins with global options (see OPTIONS below for details). The global options are followed by one or more commands. Each command should begin with -- by itself as a command-line argument, to separate it from the following commands. (The
-- before the first command is optional.) The command itself starts with command-specific options, if any, followed by the command name and any arguments."

Right now there is no proper way to supply opts for batch_mode in ovsclients_impl.py. The parameters taken are for command specific opts only. This need to be fixed so that we can add global options for batch mode execution.