Some distributions (notably, debian bookworm) have deprecated the
`python` interpreter in favor of `python3`. Since our scripts are
python3 anyway, use the proper numbered version in shebang to make
scripts easily executable.
(cherry picked from commit 480dcdef9a)
This commit extends the 'doth' system test with a set of Strict/Mutual
TLS related checks.
This commit also makes each doth NS instance use its own TLS
certificate that includes FQDN, IPv4, and IPv6 addresses, issued using
a common Certificate Authority, instead of ad-hoc certs.
Extend servers initialisation timeout to 60 seconds to improve the
tests stability in the CI as certain configurations could fail to
initialise on time under load.
