Curtin Userdata customization: add packages needed by Juju and Ansible

#
#  Xenial: add a couple of packages needed by Juju and Ansible
#

diff -c curtin_userdata_ubuntu_amd64_generic_trusty_csd curtin_userdata_ubuntu_amd64_generic_xenial_csd
*** curtin_userdata_ubuntu_amd64_generic_trusty_csd     2016-09-29 15:57:50.272409541 +0200
--- curtin_userdata_ubuntu_amd64_generic_xenial_csd     2016-09-29 15:57:36.176630139 +0200
***************
*** 28,33 ****
--- 28,35 ----
    timezone_02_set: ["curtin", "in-target", "--", "sh", "-c", "dpkg-reconfigure --frontend noninteractive tzdata"]
    limits_01_add: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo '*  soft  nofile  100000' >> /etc/security/limits.conf ; /bin/echo '*  hard  nofile  100000' >> /etc/security/limits.conf"]
    ifaceeth0_01_preup: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo 'pre-up  [ -z `cat /proc/net/bonding/* | grep Slave | grep eth0` ] && true ' >> /etc/network/interfaces.d/eth0.cfg"]
+   package_01_update_install: ["curtin", "in-target", "--", "sh", "-c", "apt-get update --quiet && apt-get --assume-yes install python"]
+   package_02_update_install: ["curtin", "in-target", "--", "sh", "-c", "apt-get update --quiet && apt-get --assume-yes install aptitude"]
  
  power_state:
    mode: reboot