LVM: update iscsi target on volume attach

This patch updates the existing iSCSI target for a LVM volume during
attach.  This is necessary in the event that a user extended the volume
after creation so that the correct size is visible to the host.

This adds support only for tgtadm.  Other changes may be needed for
ietadm/lioadm to provide the same functionality.

Change-Id: I185a90ffc4d50dd9f91381df07289476fa792043
Closes-Bug: #1248415
Use a *args pass-in instead of a list one

Change-Id: Ieef972f413dcf444d26c15a02d1993acf7cbb079
Merge "LVM: update iscsi target on volume attach"
Merge "Use a *args pass-in instead of a list one"