When a share is mounted on the same host as the manila-share
process, the kernel prevents us from destroying the
mount directory until the share has been cleanly unmounted
from the host. Kernel mounts can take a few seconds to get
unmounted fully especially when there are a lot of
linux namespaces that the mountpoint has been shared to.
Add a retry on these operations to harden the deletion
process and prevent spurious failures.
Change-Id: I3c1a2ec19d6bc18638db0875519ce60f2c89f33a
Closes-Bug: #1903773
Related-Bug: #1896672
Signed-off-by: Goutham Pacha Ravi <gouthampravi@gmail.com>