Fix modifications detection for build & install images
Fix modifications detection for build & install images

The committed image after running vMX install has an additional layer
containing the modifications done during installation. The previous
layers are the same though. When comparing the layers of the previously
tagged image with the current build, we must omit the last layer.

bdreisbach/vrnetlab,bdreisbach/vrnetlab,plajjan/vrnetlab,plajjan/vrnetlab