controller: should respect the StorageReserved setting of Longhorn

[Vicente-Cheng]

Problem:
Should update the StorageReserved for extra disks.
before fixing (this is disk related info on nodes.longhorn.io)

spec:
  allowScheduling: true
  disks:
    a827440145f11f652f00f2a6ae656ed0:
      allowScheduling: true
      diskType: filesystem
      evictionRequested: false
      path: /var/lib/harvester/extra-disks/a827440145f11f652f00f2a6ae656ed0
      storageReserved: 0
      tags: []

After fixing

spec:
  allowScheduling: true
  disks:
    a827440145f11f652f00f2a6ae656ed0:
      allowScheduling: true
      diskType: filesystem
      evictionRequested: false
      path: /var/lib/harvester/extra-disks/a827440145f11f652f00f2a6ae656ed0
      storageReserved: 3221225472
      tags: []

Solution:
get the Longhorn storage reserved settings to calculate the correct value

Related Issue:
harvester/harvester#5042

Test plan:
make sure the storageReserved is the correct value. (default is 30%)

[votdev]

Would it make sense to add a comment here to show where this default value comes from? E.g. this line.

[votdev]

Longhorn is the product name, so it should be in uppercase. The same applies to other occurrences.

Suggested change

	logrus.Warnf("Failed to get longhorn setting %s: %v", longhornStorageReservedSettings, err)
	logrus.Warnf("Failed to get Longhorn setting %s: %v", longhornStorageReservedSettings, err)

[Vicente-Cheng]

Thanks @votdev for reviewing it.

I thought maybe we did not need this PR. Confirming with LH team.

[Vicente-Cheng]

drop this because we do not need storage reserved as default for extra disks