Enable all test apps to fail during init or with OOM

The environment variable $FAIL_INIT now causes any of the test apps
to fail during initialisation, although what constitutes
initialisation depends on the application type.

The environment variable $FAIL_OOM now causes any of the test apps to
repeatedly exhaust the heap at application runtime until the JVM is
killed.

Document the failure support in the README as well as the
use of manifest.yml to provide default cf push parameters.

[#52722891] [#52853589]
Merge 52722891-generate-failures-in-all-test-apps to master

[#52722891]