automation: install awscli and python3-boto3 packages

This provides the `aws` command-line utility as well as a Python
library for interacting with AWS. It is useful to have these packages
installed in AMIs so you can easily interact with other AWS services.

Differential Revision: https://phab.mercurial-scm.org/D6914

contrib/automation/hgautomation/linux.py

@@ -210,6 +210,7 b' fi'
 sudo apt-get update
 
 PACKAGES="\
+    awscli \
     btrfs-progs \
     build-essential \
     bzr \
@@ -251,6 +252,7 b' PACKAGES="\\'
     python-pygments \
     python-subversion \
     python-vcr \
+    python3-boto3 \
     python3-dev \
     python3-docutils \
     python3-fuzzywuzzy \