Prior to this commit it was possible for two @BootstrapWith annotations
to be 'present' on a test class -- for example, via competing custom
composed annotations. However, only one of the annotations will ever be
used to bootstrap the TestContext Framework. Thus, in such scenarios
one of the annotations will be silently ignored.
This commit introduces a check for such scenarios. BootstrapUtils'
resolveTestContextBootstrapper() method now throws an
IllegalStateException if more than one @BootstrapWith annotation is
'present' on a given test class.
Issue: SPR-12602
e85e9768c5