Curtin Userdata customization: add "sudoer" user and set its password

# Add an extra user, set password, add to sudoers
#   Apparently, "ubuntu" user is not yet created, by the time late_commands runs

# Addendum: handling password hashes, based on:
# http://unix.stackexchange.com/questions/52108/how-to-create-sha512-password-hashes-on-command-line
# 
# Get hash for password "paperino":
#  python -c "import crypt, getpass, pwd; print crypt.crypt('paperino')"
# Check a given hash to verify it corresponds to some password:
# - select the hash portion up to the end of the 'salt', namely the
#   piece of string comprised between $6$ and the next '$' character
# For example:
#  python -c "import crypt, getpass, pwd; print crypt.crypt('paperino', '\$6\$Ck.Gim7WqVzsv8j9\$')"

diff -c curtin_userdata_ubuntu_amd64_generic_trusty curtin_userdata_ubuntu_amd64_generic_trusty_with-csduser 

*** curtin_userdata_ubuntu_amd64_generic_trusty 2016-09-22 11:08:45.042776292 +0200
--- curtin_userdata_ubuntu_amd64_generic_trusty_with-csduser    2016-09-22 10:46:55.207425027 +0200
***************
*** 24,29 ****
--- 24,32 ----
    driver_06_depmod: ["curtin", "in-target", "--", "depmod"]
    driver_07_update_initramfs: ["curtin", "in-target", "--", "update-initramfs", "-u"]
  {{endif}}
+   user_01_create: ["curtin", "in-target", "--", "sh", "-c", "/usr/sbin/useradd -m csdcloud"]
+   user_01_pass: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo csdcloud:'$6$t8dFheE5qQM.7yVP$1r8rmUCtYOiBAvEcK7EZpIMtiLTgfC2FdBH04rF/Qy8YBfK1fEjbGxZhhpcR2KkDtGj7jbkbm/7eWtQOVER1R1' | /usr/sbin/chpasswd -e"]
+   user_01_sudo: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo 'csdcloud    ALL=(ALL:ALL) ALL' > /etc/sudoers.d/csdcloud"]
    timezone_01_config: ["curtin", "in-target", "--", "sh", "-c", "ln -sf /usr/share/zoneinfo/Europe/Vatican /etc/timezone"]
    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"]