Xenial: update python package

imgtool 1.6.0 doesn't exist, lets install a working version.

Change-Id: Id2539cb29c42868a99b1dd4c215e684bbad9b321

Signed-off-by: Benjamin Copeland <ben.copeland@linaro.org>
Change-Id: I850e0af156e854ed3a2a66d6ecc7c9ccc0d13bab
1 file changed