Add content tests in TestDdevFullSiteSetup, fixes #677

[rfay]

The Problem/Issue/Bug:

We have long had a set of tests that carefully does a ddev start and ddev import-db and `ddev import-files on several CMSs... but never checks to see if each CMS responds appropriately. OP#677.

How this PR Solves The Problem:

Since this has been neglected for some time there are a few things that will have to be done for basic functionality, and a few that should probably be done just as an update mechanism.

• Drupal 6 project needs to use php 5.6. It currently uses php 7.0, so can't work. This may be done with an additional app.Config() probably.
• Backdrop doesn't come up at all because our test setup doesn't have a config directory
• TYPO3 doesn't work right because we're using a not-yet-installed codebase.
• The TYPO3 test should use TYPO3 v9 LTS, with a full db, not just the backend.
• We are going to detect Wordpress in a subdirectory, so we need that as an additional test CMS IMO. @alkymst recommends using Bedrock to stand in for this technique.
• Improve healthcheck behavior (and output) for ddev-webserver. It now shows in docker inspect what the actual healthcheck issue is. We now check for /var/www/html being "sane" and for mysql being accessible.
• Add php-fpm slowlog reporting to ddev-webserver
• Add mariadb slowlog output in ddev-dbserver

Additional changes:

• ddevapp_test.go tests are adjusted to assume that no project is running (and they start it themselves) and they leave the project Down (with database deleted).

Manual Testing Instructions:

Mostly this will be the automated test, but there are some features to manually test:

• Use docker inspect to view the health status of a starting webserver. It shows the actual status of 3 different things.

Automated Testing Overview:

• Add TestDdevFullSiteSetup() to import-db, import-files, and check a dynamic URL.

Related Issue Link(s):

OP #677

Release/Deployment notes:

[andrewfrench]

This looks great and adds a lot of confidence in behavior that we didn't have before. Will the WordPress-in-a-directory stuff be added to this PR?