Comment 7 for bug 1475038

The issue here may be that vivid libegl1-mesa-drivers is a dummy transitional package. So there is no libegl1-mesa-drivers-lts-vivid package.
This would cause some sources to be ftbfs in 14.04.3, likely 1st. block of -
libcogl15 : Depends: libegl1-mesa-drivers

If libwayland-egl1-mesa-lts-vivid is manually added to image or made a dep of affected the runtime should be ok (though the sources would remain ftbfs.
Maybe a dummy libegl1-mesa-drivers-lts-vivid would do?? (no clue here...