Build fails with Java 11

[smoyer64]

Some combination of JUnit 5 and the MockitoExtension leads to the following errors (one example included):

[ERROR] exitsIfRequiredBrokerUrlParameterIsMissing  Time elapsed: 0.001 s  <<< ERROR!
org.mockito.exceptions.base.MockitoException:
Unable to initialize @Spy annotated field 'messageProcessor'.
Unable to create mock instance of type 'MessageProcessor'
Caused by: org.mockito.exceptions.base.MockitoException: Unable to create mock instance of type 'MessageProcessor'
Caused by: org.mockito.creation.instance.InstantiationException:

Our dependency on the resteasy-jackson2-provider brings in version 14.0 of Google's guava library (which is ancient). This library uses internal reflection methods that produce the following warnings:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.google.inject.internal.cglib.core.$ReflectUtils$1 (file:/usr/share/maven/lib/guice.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of com.google.inject.internal.cglib.core.$ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release