Added mountinfo changes to node_exporter (#1417)

Use the extra information gleaned from the mountinfo file to add
a 'mountaddr' field for NFS metrics. This helps prevent prometheus from
ignoring mounts that come from the same URL, but are actually from
different IP addresses.

This commit also rebases to current master

Signed-off-by: Dipack P Panjabi <dpanjabi@hudson-trading.com>

CHANGELOG.md

@@ -8,11 +8,13 @@
     - `node_md_disks_active` is removed
     - `node_md_disks` now has a `state` label for "fail", "spare", "active" disks.
     - `node_md_is_active` is replaced by `node_md_state` with a state set of "active", "inactive", "recovering", "resync".
+* Additional label `mountaddr` added to NFS device metrics to distinguish mounts from the same URL, but different IP addresses. #1417
 
 ### Changes
 
 * [CHANGE] Add `--collector.netdev.device-whitelist`. #1279
 * [CHANGE] Refactor mdadm collector #1403
+* [CHANGE] Add `mountaddr` label to NFS metrics. #1417
 * [FEATURE] Add new schedstat collector #1389
 * [ENHANCEMENT] Include additional XFS runtime statistics. #1423
 * [ENHANCEMENT] Report non-fatal collection errors in the exporter metric. #1439