Error Detaching Volume on GlusterFS Primary Storage

##### ISSUE TYPE
* Bug Report

##### COMPONENT NAME

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Primary Storage (GlusterFS)
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##### CLOUDSTACK VERSION

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4.17.1.0
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##### CONFIGURATION

##### OS / ENVIRONMENT

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CentOS Linux 7 (Core)
qemu-img version 2.12.0
glusterfs 6.1

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##### SUMMARY

Can't detach volumes created on GlusterFS primary storage from VM. Tested on two different cloudstack installations. Everything works fine with other primary storage types. The volume can be detached and removed if the VM status is stopped but not when running.

##### STEPS TO REPRODUCE

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- Create GlusterFS Primary Storage with tag
- Create Disk Offering that uses just crated GlusterFS Primary Storage's tag.
- Create Volume using just created Disk Offering
- Attach Volume to VM
- Detach Volume from VM

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##### EXPECTED RESULTS

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- Success detaching Volume

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##### ACTUAL RESULTS

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- (test-detach) Failed to detach volume test-detach from VM test-vm-for-gluster ; com.cloud.exception.InternalErrorException: disk: /mnt/b440b605-a876-35f8-be84-2b5696650654/5605035d-e060-42a6-89a1-6f9c949463fc is not attached before

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Start by reproducing the detach flow described in the issue with GlusterFS primary storage on a running VM, using the listed CentOS, qemu-img, and glusterfs environment. Trace the source of the “is not attached before” error and compare it with other primary-storage types. Done means the volume detaches successfully while the VM is running and the reported scenario is covered by regression testing.

Written by the indexing model from the issue text.