poky.conf: Update SANITY_TESTED_DISTROS to match autobuilder
The autobuilder workers change over time, update the sanity testing list
to match the current autobuilder workers OS list.
(From meta-yocto rev: e1b515ec9d5c6b1b21d27db1ec413088398d538b)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>