Issue 2825: Fix gradle.dependencies related to PR 2792

[RaulGracia]

Motivation

Fixes gradle build from breaking changes in PR #2792 by strictly matching both gradle and maven dependencies.

Changes

Revert log4j and bouncycastle dependencies to their original version, to strictly match what we is defined in pom.xml.
Upgraded slf4j to match what is defined in pom.xml.

How to verify it

Run gradlew build has been also manually on a local VM:

/gradlew bookkeeper-server:test --tests="org.apache.bookkeeper.client.*" -Dtestlogger.theme=plain
...
<============-> 98% EXECUTING [15m 52s]
> :bookkeeper-server:test > 252 tests completed, 1 skipped

Master Issue: #2825

[RaulGracia]

@pkumar-singh @eolivelli please, could you check via gradlew that this also works in your setting? I want to be sure that everything is green before going any step further.

[eolivelli]

checking locally now

[pkumar-singh]

@RaulGracia Trust pipeline to test. Actually If you see, jobs moved to gradle are stable enough. That are Bookie tests and client tests. Most of important aspect of gradle migration as I am doing it is.

1. No change should be breaking.
2. Should do what maven does and does correctly, but does in isolation not affecting maven.
3. Do not modify any source code/test code.
4. Gradle should pull exact same dependencies as gradle does right or wrong.That means more important to be consistent with maven than be right.
5. It means If tests are failing then either tests are flaking or PR has issues.

[RaulGracia]

Superseded by #2816.