fix 500 errors and updated to 7.x gluster release

[marcelo-ochoa]

Hi:
I am configuring a Docker Swarm cluster together with GlusterFS, when I am trying to add some monitoring tool based on Grafana/Prometheus I found your exporter.
It works OK in stand-alone mode but when I running at our servers I found some 500 errors, similar to #16 .
In our cases is connected to Gluster Volumes with multiples mount points, for example:
`8 error(s) occurred:

• collected metric gluster_mount_successful label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/f2efb854877dfeda195ba193a6babcc355ca99fdcad163d7d017fe516f2968fe" > label:<name:"volume" value:"localhost:unifi/db" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_volume_writeable label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/f2efb854877dfeda195ba193a6babcc355ca99fdcad163d7d017fe516f2968fe" > label:<name:"volume" value:"localhost:unifi/db" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_mount_successful label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/cf17c635315406a6712258219b794d10c6ae552ae93a93b22d9f6e34cd1b9102" > label:<name:"volume" value:"localhost:unifi/data" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_volume_writeable label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/cf17c635315406a6712258219b794d10c6ae552ae93a93b22d9f6e34cd1b9102" > label:<name:"volume" value:"localhost:unifi/data" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_mount_successful label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/a6fa8065851be6a988798594e0c494aa48a0dbfa4326febaa5cdcf90ddb589f6" > label:<name:"volume" value:"localhost:unifi/db" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_volume_writeable label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/a6fa8065851be6a988798594e0c494aa48a0dbfa4326febaa5cdcf90ddb589f6" > label:<name:"volume" value:"localhost:unifi/db" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_mount_successful label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/bf196d84b6e1f4d37224e11e4e453c98e0130df6bd38fcd483818454647ae107" > label:<name:"volume" value:"localhost:unifi/data" > gauge:<value:1 > was collected before with the same name and label values
• collected metric gluster_volume_writeable label:<name:"mountpoint" value:"/var/lib/docker/plugins/3605e14efb9baa6e5a3f68e644cdaf7b175ee43cfc64e4aa097c0676af376d1d/propagated-mount/bf196d84b6e1f4d37224e11e4e453c98e0130df6bd38fcd483818454647ae107" > label:<name:"volume" value:"localhost:unifi/data" > gauge:<value:1 > was collected before with the same name and label values
  `
  they are related to Docker volume Plugin used by Swarm Services.
  Anyway this PR fix that problem ignoring mounts points starting with /var/lib/docker/plugins/, also have an update on the code to work with Gluster 7.x release.
  Best regards, Marcelo.

[ofesseler]

Hi Marcelo,

did you consider using the exporter developed by the glusterfs community mentioned in #40 ? If this won't suit your needs, you are very welcome to contribute to this project.

Regards, Oli

[marcelo-ochoa]

I'll check ASAP, do you know if there are some Grafana dashboards to visualize that exporter?
Best regards, Marcelo.