allow exists can variodic

[charsyam]

today, redis changed exists command can be variodic

request> exists ab a c
response> :3

but this feature just is in unstable.
@manjuraj Does twemproxy prefer to follow unstable branch of redis ? or stable branch?

[manjuraj]

I think we should wait for the command to be supported in stable branch before supporting them in twemproxy.

[charsyam]

@manjuraj Yes, I agree with you.That's why I asked you about it :)

[charsyam]

@manjuraj Redis 3.0.3 is out. and It contains variadic exists.
so it's time to merge this feature :)

[charsyam]

@manjuraj Please review this :)
(and I just rebase this. not code changed.)
I think we have a problem about current CI testing.

[charsyam]

@manjuraj ping Redis already contains variodic :)

[charsyam]

@manjuraj ping

[charsyam]

ping @manjuraj

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[TysonAndre]

#599 implements support for many newer redis commands, including this change to exists - I implemented it the same way without seeing this old pr

[TysonAndre]

#599 implements support for many newer redis commands, including this change to exists - I implemented it the same way without seeing this old pr

I was added as an external collaborator this week - #599 was merged.