Add support for NO_NGINX_IPV6 env variable

[Bojan023]

As per issue #68, on hosts with IPv6 disabled nginx will crash. This PR fixes this bug by adding support to force nginx to only listen to IPv4 by setting the env variable NO_NGINX_IPV6. If it is not set, Bash automatically ignores the conditional statement and skips it. Therefore, this PR should be transparant to current deployments.

[Bojan023]

Apparently there is still a bug, I'm looking into it :)

[Bojan023]

All good now, works as expected!

I also needed to add perl-net-ssleay in 8547f92 and perl-io-socket-ssl in 3bde469 to get rid of this error:

Can't locate IO/Socket/SSL.pm in @INC (you may need to install the IO::Socket::SSL module)

EDIT: still a bug, see below

[Bojan023]

Unfortunately I encounter this error which doesn't make sense given the current Dockerfile where XML::Simple is being installed:

Can't locate XML/Simple.pm in @INC (you may need to install the XML::Simple module) (@INC contains: /usr/local/lib/perl5/site_perl /usr/local/share/perl5/site_perl /usr/lib/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5/core_perl /usr/share/perl5/core_perl) at /usr/bin/dmarcts-report-parser.pl line 69.

Any suggestions on how to fix this?

[Bojan023]

Fixed, works as intended now