Pass ARCH to build system.
Added support for ARCH environment variable.
Pass ARCH to sudo environment.
Use ARCH from environment, if specified (default to i386).
Removed --linux-flavour (use default).
Merge branch 'feature-select-build-architecture'

* feature-select-build-architecture:
  Removed --linux-flavour (use default).
  Use ARCH from environment, if specified (default to i386).
  Pass ARCH to sudo environment.
  Added support for ARCH environment variable.
  Pass ARCH to build system.
Do not check Valid-Until if we are building from snapshot.debian.org.