Fix failing test

The -XX option got out of step with the testcase.

[#51561265]
Improve killjava

Improve the regex used to match processes. Also log the process
tree before and after issuing the kill command.

[#51899933]
Improve Play detection

As well as a start script, a Play application now also needs a
suitable Play JAR in the lib directory.

Add Play to the README.

[#51899933]
Merge 51899933- to master

[#51899933]
Fix Play documentation

[#51899933]
Merge 51899933- to master

[#51899933]
Test detection when no containers match

The JRE detect result (which is always non-nil for OpenJdk.detect)
does not determine the outcome of the buildpack's detect. There must
be at least one container which returns non-nil from detect before the
buildpack's detect will return any tags. Add a test to check this.

[#52289857]
Merge 52289857-improved-detection-logic to master

[Completes #52289857]
Reduce code duplication for code climate

[#52541875]
Merge 52541875-code-climate to master

[#52541875]