Fix harmless startup errors

[casperklein]

Description

When restarting the container (docker restart mailserver), depending on someones setup, the following errors may be displayed:

rm: cannot remove '/etc/cron.d/clamav-freshclam': No such file or directory

Error: sed -i /^smtpd_recipient_restrictions = / s/, reject_rbl_client zen.spamhaus.org// /etc/postfix/main.cf
Error: sed -i -r -e s|^(MinProtocol).*|\1 = TLSv1| -e s|^(CipherString).*|\1 = DEFAULT@SECLEVEL=1| /usr/lib/ssl/openssl.cnf
Error: sed -i -r s|^(smtpd_tls_chain_files =).*|\1 /etc/dms/tls/key /etc/dms/tls/cert| /etc/postfix/main.cf
Error: sed -i -r -e s|^(ssl_key =).*|\1 </etc/dms/tls/key| -e s|^(ssl_cert =).*|\1 </etc/dms/tls/cert| /etc/dovecot/conf.d/10-ssl.conf

These errors are harmless and are only triggered, because the file deletion/modification already took place on the first container start.

To bypass this, a marker file CONTAINER_START is created after the container has started.

sedfile checks if that file exists. If so, no error is displayed on a failure.
There may be circumstances, where sedfile should fail, regardless of the container state (fresh or restarted). For that, pass --strict as first parameter to sedfile. At the moment this is only the case for the delmailuser script.

Fixes #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change that does improve existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes