shared/instancewriter/instance/file/info: Adds FileInfo for os.FileInfo implementation
shared/instancewriter/instance/file/info: Adds FileInfo for os.FileInfo implementation

Used to generate 'fake' file info when streaming block devices into a tarball.

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

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