HDDS-12165. Refactor VolumeInfoMetrics to use getCurrentUsage

[adoroszlai]

What changes were proposed in this pull request?

1. Refactor VolumeInfoMetrics to fetch volume usage with a single call, instead of getting individual values separately.
2. Fix wrong Capacity and TotalCapacity. Used + Available != Capacity, because Used only includes the space used by the HDDS data dir. Capacity is already queried from the filesystem, so we should display that.

https://issues.apache.org/jira/browse/HDDS-12165

How was this patch tested?

Started ozone compose cluster, created keys using Freon.

Checked Datanode web UI, verified that volume info is present.

Before:

After:

Checked metrics in JMX endpoint, verified that metrics keys are the same as before. Values are similar, except capacity, which is correct with the patch (TotalCapacity matches the value reported by df (times 1024, since it reports 1K blocks)).

Before:

{
  "name" : "Hadoop:service=HddsDatanode,name=VolumeInfoMetrics-/data/hdds",
  "modelerType" : "VolumeInfoMetrics-/data/hdds",
  "tag.Context" : "ozone",
  "tag.StorageType" : "DISK",
  "tag.DatanodeUuid" : "9ab8037b-59f4-4f99-b762-8a33649c6f11",
  "tag.StorageDirectory" : "/data/hdds/hdds",
  "tag.VolumeState" : "NORMAL",
  "tag.VolumeType" : "DATA_VOLUME",
  "tag.Hostname" : "0f71994a6169",
  "DbCompactLatencyNumOps" : 0,
  "DbCompactLatencyAvgTime" : 0.0,
  "TotalCapacity" : 49547334340,
  "Capacity" : 49497374720,
  "Available" : 49392513024,
  "Containers" : 1,
  "LayoutVersion" : 1,
  "Used" : 104861696,
  "Committed" : 968884224,
  "Reserved" : 49959620
}

After:

{
  "name" : "Hadoop:service=HddsDatanode,name=VolumeInfoMetrics-/data/hdds",
  "modelerType" : "VolumeInfoMetrics-/data/hdds",
  "tag.Context" : "ozone",
  "tag.StorageType" : "DISK",
  "tag.DatanodeUuid" : "1bbe31d4-9dd9-4fcf-93aa-fd4717876414",
  "tag.VolumeState" : "NORMAL",
  "tag.VolumeType" : "DATA_VOLUME",
  "tag.StorageDirectory" : "/data/hdds/hdds",
  "tag.Hostname" : "f1c5efee2f91",
  "DbCompactLatencyNumOps" : 0,
  "DbCompactLatencyAvgTime" : 0.0,
  "Committed" : 968884224,
  "LayoutVersion" : 1,
  "Containers" : 1,
  "Capacity" : 499546271036,
  "Available" : 49390276608,
  "Used" : 104861696,
  "Reserved" : 49959620,
  "TotalCapacity" : 499596230656
}

[ashishkumar50]

@adoroszlai, Thanks for the refactor, LGTM.

[adoroszlai]

Thanks @ashishkumar50 for the review.