Update the existing tests to use the relocated `spring-boot-test`
classes. Restructuring was achieved using the following command:

find . -type f -name '*.java' -exec sed -i '' \
-e s/org.springframework.boot.test.ConfigFileApplicationContextInitializer/\
org.springframework.boot.test.context.ConfigFileApplicationContextInitializer/g \
-e s/org.springframework.boot.test.EnvironmentTestUtils/\
org.springframework.boot.test.util.EnvironmentTestUtils/g \
-e s/org.springframework.boot.test.IntegrationTest/\
org.springframework.boot.test.context.IntegrationTest/g \
-e s/org.springframework.boot.test.IntegrationTestPropertiesListener/\
org.springframework.boot.test.context.IntegrationTestPropertiesListener/g \
-e s/org.springframework.boot.test.OutputCapture/\
org.springframework.boot.test.rule.OutputCapture/g \
-e s/org.springframework.boot.test.SpringApplicationConfiguration/\
org.springframework.boot.test.context.SpringApplicationConfiguration/g \
-e s/org.springframework.boot.test.SpringApplicationContextLoader/\
org.springframework.boot.test.context.SpringApplicationContextLoader/g \
-e s/org.springframework.boot.test.SpringBootMockServletContext/\
org.springframework.boot.test.mock.web.SpringBootMockServletContext/g \
-e s/org.springframework.boot.test.TestRestTemplate/\
org.springframework.boot.test.web.client.TestRestTemplate/g \
-e s/org.springframework.boot.test.WebIntegrationTest/\
org.springframework.boot.test.context.web.WebIntegrationTest/g {} \;

See gh-5293