MINOR: Fix warnings in build

[sjhajharia]

Currently on running ./gradlew clean jar on trunk, the following two warnings pop up:

> Task :metadata:compileTestJava
Note: ~/kafka/metadata/src/test/java/org/apache/kafka/controller/metrics/QuorumControllerMetricsTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

> Task :server:compileTestJava
Note: ~/kafka/server/src/test/java/org/apache/kafka/server/AssignmentsManagerTest.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

The PR attempts to fix the same

[chia7712]

@sjhajharia thanks for this patch. Could you fix other warnings as well?

> Task :streams:compileTestJava
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: /home/chia7712/project/kafka/streams/src/test/java/org/apache/kafka/streams/processor/internals/TaskManagerTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

> Task :transaction-coordinator:compileTestJava
Note: /home/chia7712/project/kafka/transaction-coordinator/src/test/java/org/apache/kafka/coordinator/transaction/TransactionLogTest.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

> Task :connect:runtime:compileTestJava
Note: /home/chia7712/project/kafka/connect/runtime/src/test/java/org/apache/kafka/connect/runtime/WorkerSinkTaskTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.