Add tests for nginx-ssl-util and nginx-ssl-util-nopcre using (fake)chroot.
Clean the code up making nginx-ssl-util a header file.
Both changes are for better (future) code quality only.

There are minor functional improvements:
* fix compiler error of gcc7 by using std=c++17
* fix error if there is no lan/loopback interface
* notice instead of error message if there is no default server
* add ipv6-prefix-assignment.*.local-address.address for LAN
* add CONFLICTS in Makefile for choosing the right version
* add cast to release of unique_ptr to avoid warning
* add version message to help message

Signed-off-by: Peter Stadler <peter.stadler@student.uibk.ac.at>

* Do not destroy the iterator twice if cur==this (segfault).
* Do not add the delimiter clim=='\0' when creating the SSL directives.
* Set the right SSL_SESSION_CACHE_ARG for nginx-util get_env.
* Remove static from the constexpr that are used only for Line::build.
* Concat strings instead of appending them for not using a non-const ref
(to remove some warnings of clang-tidy -checks=google-runtime-references)

Signed-off-by: Peter Stadler <peter.stadler@student.uibk.ac.at>

This can do the main work of nginx/nginx-ssl init script.
For nginx-ssl it can create selfsigned certificates, too.
It uses libpcre and libopenssl iff nginx(-ssl) uses them.

Signed-off-by: Peter Stadler <peter.stadler@student.uibk.ac.at>