[CI] Port CI fixes from the 1.2.0 branch (#6050)

* Fix a unit test on CLI, to handle RC versions

* [CI] Use mgpu machine to run gpu hist unit tests

* [CI] Build GPU-enabled JAR artifact and deploy to xgboost-maven-repo

tests/python/test_cli.py

@@ -124,6 +124,8 @@ eval[test] = {data_path}
         v = xgboost.__version__
         if v.find('SNAPSHOT') != -1:
             assert msg.split(':')[1].strip() == v.split('-')[0]
+        elif v.find('rc') != -1:
+            assert msg.split(':')[1].strip() == v.split('rc')[0]
         else:
             assert msg.split(':')[1].strip() == v