shared/instancewriter/instance/tar/writer: Adds ignoreGrowth arg to WriteFile
shared/instancewriter/instance/tar/writer: Adds ignoreGrowth arg to WriteFile

This is to allow us to restore the old behavior of export that only reads up to the original size of a file that is being grown during backup.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

Skarlso/lxd,lxc/lxd,stgraber/lxd,mjeanson/lxd,hallyn/lxd,Skarlso/lxd,lxc/lxd,hallyn/lxd,Skarlso/lxd,mjeanson/lxd,mjeanson/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,Skarlso/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd