Parent: updated to docker-nginx 7.0, using nginx-light instead of full

Upstream Changes:
https://github.com/behance/docker-nginx/releases/tag/7.0.0

Parent: updated to docker-nginx 6.4.0, fixed tests, fixed Alpine variant

• Update parent to 6.4 (https://github.com/behance/docker-nginx/releases/tag/6.4.0), which updated to base 1.6
• Fixed bad pdo_pgsql goss test to actually look for presence of extension
• Fixed Alpine build, using promoted mainline php7 packages (from community)
• Added Alpine back into travis matrix

NewRelic: updated to 6.9.0.182

Changes:
https://docs.newrelic.com/docs/release-notes/agent-release-notes/php-release-notes/php-agent-690182

Redis: update to extension 3.1 in stable channel

• https://pecl.php.net/package-changelog.php?package=redis&release=3.1.0
• Unifies extension version across 5.6, 7.0 PHP engines
• Integrates lazy connection management (finally!)

Secure Headers: Added new defaults

Updating docker-nginx container version, which includes new secure HTTP headers.

Adding a new http_headers.conf file with some secure http headers, as recommended by https://securityheaders.io/

Added HTTP Headers:

X-XSS-Protection 1; mode=block
X-Content-Type-Options nosniff

Secure Headers: Added new defaults

Updating docker-nginx container version, which includes new secure HTTP headers.

Adding a new http_headers.conf file with some secure http headers, as recommended by https://securityheaders.io/

Added HTTP Headers:

X-XSS-Protection 1; mode=block
X-Content-Type-Options nosniff

Optimizations: combine cross-variant scripts, tightened tests

• Using latest parent (6.2)
• Additional opcache configuration via env variables
• Tuning/tweaks now use same commands across all variants
• Base tests now run in all variants
• Relying on single (non-7.0) symlink for start command
• Upgraded NewRelic on beta version (only), which is now officially supporting PHP 7.1

Yaml/Redis: moved to pecl-installed stable versions for PHP 7 (and 5.6 for legacy)

• Swapped from PPA to PECL-maintained stable versions
• Added additional tests for default-disabled extensions
• Added hold for untargetted versions of PHP

Legacy: patch for overwritten mod .ini files

Merge pull request #109 from mannytoledo/fix/phpmodules

Fix copy of php modules

Production Tweaking Roll-up

• Documentation: added defaults to configuration table
• Opcache: enabled by default, with time-validated timestamps for development
  • "Production mode" disables timestamp check, for a decent performance gain
• Monitoring: Added status pages for both nginx and PHP-FPM, but only enabled in-container by default
• Tweaks: increased fastcgi buffers, allowed runtime tweaking