'umount: Device is busy ' error on delete, extend and shrink operations in generic driver

[Igor Malinovskiy]

Steps to reproduce:
1. Create NFS share
2. Add access rule
3. Mount NFS share on client VM (mount path ~/test_share)
4. client_vm> dd if=/dev/zero of=test.out bs=10MB count=100
5. client_vm> cp test.out test_share/test.out
6. Perform delete/extend/shrink operation

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/200528

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/200529

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/200528
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=33fe119481b1567f7c973ebcf85b076554bda944
Submitter: Jenkins
Branch: master

commit 33fe119481b1567f7c973ebcf85b076554bda944
Author: Julia Varlamova <email address hidden>
Date: Fri Jul 10 09:06:57 2015 -0400

    Add 'retry' wrapper to manila/utils.py

    Retrying library from OpenStack Requirement is already used in Manila
    project. Add 'retry' wrapper around it which enables logging and
    checking of input param 'retries' which may be useful.

    Related-Bug: #1469068

    Change-Id: I159b6e44fec9455634d76c093036f934cf400366

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/200529
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=cf637479c9b2356e6b011c6b000c68561a1b045a
Submitter: Jenkins
Branch: master

commit cf637479c9b2356e6b011c6b000c68561a1b045a
Author: Julia Varlamova <email address hidden>
Date: Fri Jul 10 09:20:29 2015 -0400

    Retry _unmount_device in generic driver

    We get 'umount: Device is busy ' error on delete,
    extend and shrink operations in generic driver.

    Add 'retry' decorator to _unmount_device function in generic driver
    to allow driver to wait until unmounting will be possible.

    Closes-bug: #1469068

    Change-Id: I2192ed76978cd37051c8b71528ad5dcd3c222d67