Description of problem:

This is a continuation of https://bugzilla.redhat.com/show_bug.cgi?id=1874028 , because fixes in that BZ are not enough.

Current query after BZ fix looks like this:

sum by (instance) (node_filesystem_size_bytes{fstype!~"tmpfs|squashfs",mountpoint!~"/usr|/var"} - node_filesystem_free_bytes{fstype!~"tmpfs|squashfs",mountpoint!~"/usr|/var"})

But it is not enough because:
- Mountpoint at `/sysroot` is not ignored, although it is a duplicate of `/` (this one is reported at all the reproducers I could have access to)
- Mountpoint at `/etc` is not ignored, although it is a duplicate of `/` (this one is reported at my 4.6.1 own reproducer)
- nsfs mount points are not ignored, although they should (I only had this at my 4.5 reproducers, but we need to filter them out in 4.6+ as well)

The queries should be fixed to look like:

sum by (instance) (node_filesystem_size_bytes{fstype!~"tmpfs|squashfs|nsfs",mountpoint!~"/usr|/var|/etc|/sysroot"} - node_filesystem_free_bytes{fstype!~"tmpfs|squashfs|nsfs",mountpoint!~"/usr|/var|/etc|/sysroot"})


Version-Release number of selected component (if applicable):

4.6.1 and 4.5

How reproducible:

Always in certain reproducer environments

Steps to Reproduce:
1. Open console 
2. Go to nodes --> storage
3. See that calculations are still wrong

Actual results:

Calculations wrong

Expected results:

Calculations correct

Additional info:

I can easily build both 4.6.1 and 4.5 reproducers for any data needed.