Reduce size of rootfs layer and common mkfs and rsync options
Reduce size of rootfs layer and common mkfs and rsync options

Attempt to shrink the partition size for the rootfs via mkfs options
Ensure we use the same mkfs and rsync options everywhere.

Signed-off-by: Ryan Harper <7c8ea25f69f5166c51151e84bf5db678c2384828@canonical.com>

CanonicalLtd/subiquity,CanonicalLtd/subiquity