Allow for alternate ssh config location

[jfray]

Updated rtop-vis to be able to handle an ssh config other than ~/.ssh/config.

[jfray]

Not sure if you are accepting public PRs, but I figured I'd shoot this one over to you. This PR adds a command line option for using an alternate SSH config file and fixes an issue where graphs do not render if hostname -f returns a non-zero exit. It appears that hostname -f on CoreOS hosted by Vagrant has issues. The included change just uses the value from the SSH config's HostName parameter in that case.

I'm glad to add a test case if you'd like, but I noticed that there weren't any yet and didn't want to impose a test without asking you both first. Thanks for rtop-vis! I've integrated it into a basic container testing script and plan on adding more stats collectors if that's alright?

@mdevan @sebeichholz

[mdevan]

Could you split this up into two: the first one for the bug fix, and the second for the alternate ssh config location? The second one should also update the text in the usage().

[jfray]

I've updated this PR to only include the necessary changes for the alternate SSH config location and created https://github.com/rapidloop/rtop-vis/pull/7 for the hostname -f issue. Thanks!

[jfray]

Anyone? I would love to move away from my fork for this one small change.