Prior to this change, source images could introduce variation in the
the result of the bootloader element results, if the configuration
is changed later which would could re-introduce arguments not desired
which come from the source image.
Since we assert, bsaed upon user supplied input, new console configuration
we now strip the console configuration from /etc/default/grub configuration
before starting to work on putting in place the user's desired end state.
This also ends up helping reduce/remove the possibility of multiple
console elements as some were sourcing from the original source image.
Change-Id: Ia1f9987d989f1d0e1cbda619f7abdf7005b47fbc
abe2a4e239