SMBFS: Ensure the attach/disconnect operations are synchronized
SMBFS: Ensure the attach/disconnect operations are synchronized

We need to make sure that those operations are synchronized so that
the share is not disconnected while we are trying to attach a disk.

This was already done previously, but the patch adding FC support
has moved the attach method to the BaseVolumeDriver.

This change fixes this issue. Also, the decorator used for
synchronizing the operations based on the share path has been moved
to the SMBFS volume driver, as it's strictly related to it.

Change-Id: Ia840741f4fcde5e5d56020b7ee7068833095fa4c

stackforge/compute-hyperv,openstack/compute-hyperv,alexpilotti/compute-hyperv,openstack/compute-hyperv,cloudbase/compute-hyperv