Handle data path changes between versions of Lustre

[joehandzik]

@roclark has identified some pieces of data that have changed their path home between versions of Lustre. An example is some set of ldlm data that is now in sysfs instead of procfs. We need to develop a way to allow the user to specify which version of Lustre they're running, and change our expectations of data locations depending on version.

My first guess at a design would involve making structures to hold the different path options for metric search locations, and take a Lustre version argument at the command line (no argument would default to the most recent version of Lustre that we've developed for). We could then dynamically load a different path for any metric that needs it.

The unfortunate part here is that it makes our design confusing. Now, we have metrics that were in proc for some versions, and will be in sys for others. It's...not something I'm sure how to deal with, but we can thank the Lustre community later for that. :)