Prevent htmlunit from pulling in commons-logging

Update dependency management to exclude commons-logging and add
an enforcer rule to spring-boot-samples to try and prevent unwanted
commons-logging dependencies from sneaking back in again.

Closes gh-7067

spring-boot-dependencies/pom.xml

@@ -1048,6 +1048,12 @@
 				<groupId>net.sourceforge.htmlunit</groupId>
 				<artifactId>htmlunit</artifactId>
 				<version>${htmlunit.version}</version>
+				<exclusions>
+					<exclusion>
+						<groupId>commons-logging</groupId>
+						<artifactId>commons-logging</artifactId>
+					</exclusion>
+				</exclusions>
 			</dependency>
 			<dependency>
 				<groupId>net.sourceforge.jtds</groupId>