Fix “Hash sum mismatch” error in maas that can occur when a local mirror and maas' apt-proxy cache get out of sync

fix_hashsummismatch_error

#To fix bad hashInsert the following as after "late_commands:" in /etc/maas/preseeds/curtin_userdata

  prxyfix_01_cmd: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo  'Acquire::http::Pipeline-Depth 0;' > /etc/apt/apt.conf.d/99FixBadProxy"]
  prxyfix_02_cmd: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo  'Acquire::http::No-Cache true;' >> /etc/apt/apt.conf.d/99FixBadProxy"]
  prxyfix_03_cmd: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo  'Acquire::BrokenProxy    true;' >> /etc/apt/apt.conf.d/99FixBadProxy"]

#Automatically insert above into /etc/maas/preseeds/curtin_userdata using sed
sudo sed -e '/late_commands:/a  \ \ prxyfix_01_cmd: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo  '"'"'Acquire::http::Pipeline-Depth 0;'"'"' > /etc/apt/apt.conf.d/99FixBadProxy"]\n\ \ prxyfix_02_cmd: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo  '"'"'Acquire::http::No-Cache true;'"'"' >> /etc/apt/apt.conf.d/99FixBadProxy"]\n\ \ prxyfix_03_cmd: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo  '"'"'Acquire::BrokenProxy    true;'"'"' >> /etc/apt/apt.conf.d/99FixBadProxy"]' -i /etc/maas/preseeds/curtin_userdata