Exporter rewrite

[sanderdescamps]

Hi,

We were using this exporter in a large environment. But we had some performance issues. Some metrics took multiple minutes to be queried and we had holes in our data which we couldn't explain where they came from.

In the last couple weeks, I've reviewed the entire exporter and did rewrote some of the code. Bellow you have a list of the biggest changes. Unfortunately I was not able to provide full backwards compatibility. So it is not a plugin replacement and there are quite a couple of braking changes. But nevertheless, I'm wondering if you are interested in merging or if we keep the repo's separate?

You can find my work here. I still need to do some testing but it should be fully functional. You can use vcsim if you want to test.

Biggest changes:

• Add active cache which queries data from vcenter. (9x time improvement)
• Remove non-constant data from labels + Add extra metrics where needed.
• Restructure and cleanup repo
• Add datastore metrics by host
• Add possibility to use vCenter tags as metric labels
• Changed some of the CLI properties
• ....