[eos] fix banner when transport is ssh

[derekdainys]

When setting transport="ssh" the heredoc commands cause an issue because they are not a string.
This allows for heredoc commands to not be converted when using "ssh" transport

[ktbyers]

@bewing You know a lot more about this area of the code? Any objections?

[bewing]

Can we add a SSH test double class to https://github.com/napalm-automation/napalm/blob/develop/test/eos/conftest.py and possibly start testing some of the differences in behavior between the SSH and eAPI transports/drivers/devices?

[ktbyers]

@bewing Do we want to do this in conftest.py or have a separate test/eos and test/eos_ssh folder.

The latter is probably more consistent with what we did for other drivers (though we also have more code separation at the driver level between nxos and nxos_ssh (and between iosxr and iosxr_netconf).

Ultimately, I am fine with either/both (though probably have a preference for separate test folders for the different drivers+transport).

[bewing]

I also think eos_ssh folder makes more sense. I'll look at cribbing what's necessary from the existing _ssh folders and the standard EOS test double to arrange the boilerplate. @derekdainys if you can actually collect the data for the unit test it would be great - let me know on slack if you need any guidance