Background bootstrapping via "bootstrapExecutor" for  LocalContainerEntityManagerFactoryBean and LocalSessionFactoryBean/Builder

Issue: SPR-13732

Issue: SPR-12766

Prior to this commit, the codebase was using a mix of log4j.xml
and log4j.properties for test-related logging configuration. This
can be an issue as log4j takes the xml variant first when looking
for a default bootstrap configuration.

In practice, some modules declaring the properties variant were
taking the xml variant configuration from another module.

The general structure of the configuration has also been
harmonized to provide a standard console output as well as an
easy way to enable trace logs for the current module.

Prior to this commit many test utility classes and sample beans were
duplicated across projects. This was previously necessary due to the
fact that dependent test sources were not shared during a gradle
build. Since the introduction of the 'test-source-set-dependencies'
gradle plugin this is no longer the case.

This commit attempts to remove as much duplicate code as possible,
co-locating test utilities and beans in the most suitable project.
For example, test beans are now located in the 'spring-beans'
project.

Some of the duplicated code had started to drift apart when
modifications made in one project where not ported to others. All
changes have now been consolidated and when necessary existing tests
have been refactored to account for the differences.

Conflicts:
	spring-beans/src/test/java/org/springframework/beans/factory/ConcurrentBeanFactoryTests.java
	spring-beans/src/test/java/org/springframework/beans/factory/support/BeanFactoryGenericsTests.java
	spring-beans/src/test/java/org/springframework/beans/support/PagedListHolderTests.java

This renaming more intuitively expresses the relationship between
subprojects and the JAR artifacts they produce.

Tracking history across these renames is possible, but it requires
use of the --follow flag to `git log`, for example

    $ git log spring-aop/src/main/java/org/springframework/aop/Advisor.java

will show history up until the renaming event, where

    $ git log --follow spring-aop/src/main/java/org/springframework/aop/Advisor.java

will show history for all changes to the file, before and after the
renaming.

See http://chrisbeams.com/git-diff-across-renamed-directories