Bug 15303 Letsencrypt option for Debian package installations

Bug 15303 Letsencrypt option for Debian package installations

New option koha-create --letsencrypt

- installs the letsencrypt package if needed
- creates <instance>
- generates letsencrypt certificates for <instance>
- sets up a https-only website for <instance>
- redirects http to https for <instance>

! you need to enable jessie backports to install letsencrypt: add
deb http://http.debian.net/debian jessie-backports main contrib non-free
to your /etc/apt/sources.list

! this patch uses the letsencrypt staging server
to create real certificates, apply thy "LE production server" patch

Test plan:
- build a debian package with patch applied
- use apache mod_ssl
  sudo a2enmod ssl
- make sure the machine is accessible on 80 (needed for letsencrypt) and 443 from the internet
- install koha with your new package
- Put your (existing) domain options in /etc/koha/koha-sites.conf
- use koha-create with the new options:
  sudo koha-create --create-db --letsencrypt <instance>
- if you do not have the letsencrypt package installed, you will be prompted to do that
  [
    if there is no package available, a symlink to the git checkout will work:

    on your test server, get letsencrypt via git
    git clone https://github.com/letsencrypt/letsencrypt

    create a symlink from /usr/bin/letsencrypt to letsencrypt-auto
    sudo ln -s /path/to/letsencrypt/letsencrypt-auto /usr/bin/letsencrypt
  ]

- wait until setup is finished, check that you got a working OPAC and staff client with certificates
- check that http redirects to https

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>