KAFKA-10447: Migrate tools module to JUnit 5 and mockito

[ijuma]

This change sets the groundwork for migrating other modules incrementally.

Main changes:

• Replace junit 4.13 with junit-jupiter and junit-vintage 5.7.0-RC1.
• All modules except for tools depend on junit-vintage.
• tools depends on junit-jupiter.
• Convert tools tests to JUnit 5.
• Update PushHttpMetricsReporterTest to use mockito instead of powermock and easymock
  (powermock doesn't seem to work well with JUnit 5 and we don't need it since mockito can mock
  static methods).
• Update mockito to 3.5.7.
• Update TestUtils to use JUnit 5 assertions since tools depends on it.

Unrelated clean-ups:

• Remove unit from package names in a few core tests.
• Replace try/catch/fail with assertThrows in a number of places.
• Tag CoordinatorTest as integration test.
• Remove unnecessary type parameters when invoking methods and constructors.

Tested with IntelliJ and gradle. Verified that the following commands work as expected:

• ./gradlew tools:unitTest
• ./gradlew tools:integrationTest
• ./gradlew tools:test
• ./gradlew core:unitTest
• ./gradlew core:integrationTest
• ./gradlew clients:test

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[ijuma]

This test is much slower than the rest in tools, so I think it makes sense to mark it as integration.

[ijuma]

Unrelated flaky failures:

Build / JDK 15 / kafka.network.DynamicConnectionQuotaTest.testDynamicListenerConnectionCreationRateQuota
Build / JDK 8 / kafka.api.PlaintextAdminIntegrationTest.testConsumerGroups
Build / JDK 8 / org.apache.kafka.streams.integration.EosBetaUpgradeIntegrationTest.shouldUpgradeFromEosAlphaToEosBeta[true]

[omkreddy]

@ijuma Thanks for the PR. LGTM.

[ijuma]

Rebased to fix a trivial conflict. JDK 11 and JDK 8 builds passed, JDK 15 failed with 2 unrelated flaky test failures:

kafka.network.DynamicConnectionQuotaTest.testDynamicListenerConnectionCreationRateQuota
kafka.network.DynamicConnectionQuotaTest.testDynamicListenerConnectionCreationRateQuota
kafka.server.DynamicBrokerConfigTest.testPasswordConfigEncoderSecretChange