It's always False.

Ref T680

There's no need for these functions now that they're just pass throughs.

Ref T680

It's only ever True in one place, and I don't think I care about that.
We can just always log.

Ref T680

It defines some fairly common function names like "run" that I want to
use, so it makes sense to import the whole module and force us to do
"subprocess.popen" instead.

This is only ever used in one place.  It can just be an argument array
instead.  And while I'm at it, do what the TODO suggested and use
subprocess instead.

Ref T680

If we pass universal_newlines=True when we create a Popen object, the
resulting streams will be text instead of bytes (when we support python
>= 3.7, this is also called text=True).

Additionally, it's unclear to me that this was actually useful in the
first place.  We were logging the byte strings before converting them to
text.

Ref T680

This is also used in one place, so just define it as a private variable
in the class itself.  Note that it would really make a lot of sense to
also have this be a list of arguments, but in order to do that properly
we also need to change everywhere that runs a command to pass a list as
well.  That's a project for another day.

Ref T680

* It completely duplicates what the async_call method does.

* There's one caller in LogAudit that was using it totally incorrectly.
  verbose=0 doesn't matter because that argument was never getting
  passed to AsyncCmd, so it would log however it wanted regardless.
  And, rc would always be 0 because we don't wait around for the process
  to give us a valid return code so the error message would never be
  logged.

Ref T680

This doesn't really do anything interesting now.  It just returns the
singleton instance of RemoteExec, but I don't think there's much savings
to be had in doing this instead of just creating a new instance each
time.  It's not a very complicated class with lots of variables that
take time to set up.

This also allows us to get rid of all of the pylint not-callable pragmas
since that level of indirection has been removed.

Ref T680

What we really care about here is whether or not one system can ssh into
another, so all we need to do is just try to ssh without all those extra
options.

Ref T680

In general, you definitely want to do host key checking and this
option is set to "ask" by default.  However, in CTS, this means that if
you haven't ssh'd between systems first and done host key checking (or
at least responded to the ssh prompt), it will stop and ask.  This
results in test case failures.

So add this argument to just skip the host key checking and prevent
those failures.  I think this is reasonable to do in CTS, but obviously
you wouldn't want to do this elsewhere.

This fixes a pylint warning regarding naming.

TCPKeepAlive=yes and ServerAliveCountMax=3 are ssh defaults, and appear
to have been ssh defaults for a very long time.  The only reason to
specify these would be if you had your ctslab machines configured
differently, which I don't expect anyone is doing.  Thus we can just
remove these.