[SRU all] LP#1717920 -- fix ADT rebuild testing

[Andy Whitcroft]

When we added use of the autopkgtest profile to the rebuild test this
broke the rebuild test for architectures which have more flavours in
their d-i configuration than just their first flavour.  As this testing
is about testing the compiler and associated bits just turn off udebs in
this profile.

Proposing for all series we applied the previous autopkgtest profile
changes (likely all).  We do not need to respin something for this
which is not going to be spun in the cycle it is applied.

-apw