GemFire 8.0 depends on two different versions of xml-apis:xml-apis and
org.eclipse.jdt.core.compiler:ecj. This commit adds dependency
management for those two dependencies to address the dependency
convergence errors reported by Maven’s enforcer plugin.

GemFire 8.0 also depends on commons-logging and Spring Boot starters
should use jcl-over-slf4j instead. This commit adds an exclusion for
commons-logging

GemFire 8.0 depends (optionally) on spring-data-gemfire and
spring-data-gemfire depends on GemFire, i.e. there’s a dependency cycle
between the two projects. This commit breaks this cycle by adding an
exclusion for spring-data-gemfire to the dependency management for
com.gemstone.gemfire:gemfire.

This commit should be reverted once the problems with GemFire’s
dependencies have been addressed. See gh-2884.