Align Oracle docker image with the one used in the official Hive repository

[zabetak]

There is an option to initialize the metastore with different DBMS. When Oracle is used we are using the following image:
quay.io/maksymbilenko/oracle-12c

Oracle docker images are also used in the official Hive repo (for metastore and JDBC storage handler tests).

• https://github.com/apache/hive/blob/8b312d54ea206461cb50450ac95ec267aba60b21/itests/util/src/main/java/org/apache/hadoop/hive/ql/externalDB/Oracle.java#L42
• https://github.com/apache/hive/blob/8b312d54ea206461cb50450ac95ec267aba60b21/standalone-metastore/metastore-server/src/test/java/org/apache/hadoop/hive/metastore/dbinstall/rules/Oracle.java#L27

Those are using pvargacl/oracle-xe-18.4.0 image and soon (https://issues.apache.org/jira/browse/HIVE-26450) they are going to use gvenzl/oracle-xe:18.4.0-slim.

To avoid pulling images multiple times but also reproduce problems easier it would be nice to use the same Oracle docker image everywhere.

In addition using gvenzl/oracle-xe:18.4.0-slim might improve startup time since the image appears much smaller than the one currently in use (~3.7GB).

docker manifest inspect quay.io/maksymbilenko/oracle-12c |  jq '.layers[].size' | awk '{s+=$1} END {print s}'