This reverts commit d25286c5

Closes gh-20566

* pr/20566:
  Upgrade CI images to Ubuntu Bionic 20200311

Closes gh-20566

See gh-20566

Fixes gh-20531

Previously, DependencyCustomizer's ifAllResourcesPresent method
would return a customizer that added modules if any of the resources
were present. This commit corrects this behaviours so that modules are
only added if all resources are present.

Fixes gh-20418

TomcatReactiveWebServerFactory's getTomcatWebServer is described as
being a hook point the can be overrideden to return a different
TomcatWebServer or to apply additional processing to the Tomcat
server. Previously, this did not work as the method was not called
to create the TomcatWebServer instance. Instead, TomcatWebServer was
instantiated and returned directly.

This commit updates TomcatReactiveWebServerFactory to call
getTomcatWebServer to create the TomcatWebServer instance. A test
has also been added to verify that the method is now used.

Fixes gh-20386

This reverts commit 6828a15d.
The commit has been reverted as it breaks backwards compatiblity.

Fixes gh-20343

* pr/20420:
  Upgrade CI to Docker 19.03.7

Closes gh-20420

See gh-20420

* pr/20361:
  Upgrade CI images to Ubuntu Bionic 20200219

Closes gh-20361

See gh-20361

* pr/20355:
  Automate Ubuntu base image upgrade

Closes gh-20355

See gh-20355

Closes gh-20322

Closes gh-20321

Closes gh-20320

Closes gh-20198

Closes gh-20197

Closes gh-20196

Fixes gh-20134

Closes gh-20260

Closes gh-20259

Closes gh-20258

Closes gh-20257

Closes gh-20256

Closes gh-20255

Closes gh-20254

Closes gh-20253

Closes gh-20252

Closes gh-20251

Closes gh-20250

Closes gh-20249

Closes gh-20248

Closes gh-20247

See gh-20196

See gh-20198

See gh-20197