Move "yes | lvcreate" and umounting to 3.4

lvcreate prompting appears to have been moved into 6.6, so answer
the prompt. Additionally, pre-emptively umount before creating in
case the changes from EL7 which require doing so make it back.

Change-Id: I1e7ed8172d891f3dab764e524624a5cf7cd32003
Signed-off-by: Ryan Barry <rbarry@rbarry.phresus.priv>