Remove create_export from volume create

Remove create_export from volume create

Currently the LVM driver creates iscsi targets on
volume creation, even though it's only used at
attach time.  This isn't necessary and in fact
causes issues if a volume is extended because the
target information isn't currently updated after the
extend.  In addition a number of other drivers inclduing
the LIO iscsi driver require the target be created with
initiator info, so the tgt that's created initially
again isn't valid.

This change removes the create_export call from the
volume create process and makes it part of the
managers intialize_connection routine which is
more appropriate.

This change also removes the target on detach since
it's not used any longer and again as the volume may
be modified or extended.

Change-Id: I0b7dfdaf7e49a069da22f22f459861b0b49430a4
Closes-Bug: 1248947