Fix uninitialized instance variable / overridden function warnings.

[xavierholt]

Found myself cleaning up some Ruby warnings while testing a branch earlier today, so I thought I'd finish the job and help out with #344

Couple notes:

• Most changes are simply setting things to nil in initialize methods.
• Identical unindent functionality is provided by the unindent gem, so the monkeypatch version isn't needed any more.
• Part of my fix makes group_size and wait_interval publicly readable on the runners. It seemed odd to have them writeable but not readable, so I felt okay making the visibility change. If that's not okay, let me know and I'll revert that part.

[leehambley]

LGTM :) thanks for the contribution - Should I merge right now, or would you like to credit yourself in the changelog ?

[robd]

Hey - apologies for chiming in out of nowhere!

One thing I noticed here (unless I missed something) is that the unindent method is only called in one place (test/functional/backends/test_netssh.rb). I wondered if it would be better to remove the SSHKit dependency on the unindent Gem, and move the unindent method from test/unit/core_ext/test_string.rb to test_netssh.rb?

I guess the only other thing to check is whether the build is passing - see discussion here: #351

[xavierholt]

@robd: Updated with an even further simplification - scrap the unindent method entirely!

@leehambley: No need - I got credit for my actual bugfix, and this is just trivial cleanup. I'm okay to merge whenever. Not sure if #351 is relevant. It'll pass CI; the issue only shows up when running on a host with a non-empty known_hosts file (I think). Just let me know if you'd like me to rebase after the fix is in.

[robd]

scrap the unindent method entirely!

👍 Even better!

[mattbrictson]

#351 is now fixed in master. Can you rebase, please?

[xavierholt]

@mattbrictson: Rebased. Cheers!

[mattbrictson]

Acceptance tests pass. ✅

@leehambley I'll leave the merge to you.

[leehambley]

Thanks @xavierholt and for the sanity checking @mattbrictson