Update build_chroot GHC packages
Update build_chroot GHC packages

Make build_chroot more flexible about the tarballs it can download.
This make it easier to add GHC 8.0 support later.

* Use deb8 (jessie) binaries and xz tarballs where available.
  These are substantially smaller downloads.

* Upgrade from ghc 7.10.2 to 7.10.3. This fixes a number of bugs
  and a compile time speed regression.
  https://ghc.haskell.org/trac/ghc/wiki/Status/GHC-7.10.3

Signed-off-by: Brian Foley <a00e555871a6a538e97f8c44307104c884f8e869@google.com>
Reviewed-by: Viktor Bachraty <a13ea37fcfcda126dc54f94389ded93f402eee93@google.com>

mbakke/ganeti,ganeti/ganeti,ganeti/ganeti,onponomarev/ganeti,mbakke/ganeti,andir/ganeti,andir/ganeti,andir/ganeti,ganeti/ganeti,onponomarev/ganeti,mbakke/ganeti