[rb] Default http client use persistent connections

[twalpole]

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[twalpole]

This is to start a discussion on using a persistent connection by default -- sped up Sauce over SSL by about 30% on a portion of the Capybara test suite (test suite is not necessarily typical because it does a bunch of things we specifically tell users not to)

[titusfortner]

So, this should better address the issue in #5758
Also, if this works, we should probably deprecate the Remote::Http::Persistent class entirely.

I'm also really curious if Ruby is the only binding that doesn't default to keep-alive for remote connections, because if so, I'm going to need to get code out to Sauce clients on how to turn it on. :) I'll ping people on irc tomorrow.

[titusfortner]

I've verified that keep alive is turned on by default for Java and .net