[FLINK-12316][jdbc] Relax assertions

[zentol]

What is the purpose of the change

Relaxes the exception message assertion in JDBCFullTest#testEnrichedClassCastException such that it works under java 8 and 9+. The test was failing since the class names for Strings, Doubles etc. are different under Java 9.

The assertion now only checks for the part of the exception that we actually control.

[flinkbot]

Thanks a lot for your contribution to the Apache Flink project. I'm the @flinkbot. I help the community
to review your pull request. We will use this comment to track the progress of the review.

Review Progress

• ✅ 1. The [description] looks good.
  • Approved by @tillrohrmann [PMC]
• ✅ 2. There is [consensus] that the contribution should go into to Flink.
  • Approved by @tillrohrmann [PMC]
• ❓ 3. Needs [attention] from.
• ✅ 4. The change fits into the overall [architecture].
  • Approved by @tillrohrmann [PMC]
• ✅ 5. Overall code [quality] is good.
  • Approved by @tillrohrmann [PMC]

Please see the Pull Request Review Guide for a full explanation of the review process.

The Bot is tracking the review progress through labels. Labels are applied according to the order of the review items. For consensus, approval by a Flink committer of PMC member is required

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot approve description to approve one or more aspects (aspects: description, consensus, architecture and quality)
• @flinkbot approve all to approve all aspects
• @flinkbot approve-until architecture to approve everything until architecture
• @flinkbot attention @username1 [@username2 ..] to require somebody's attention
• @flinkbot disapprove architecture to remove an approval you gave earlier

[tillrohrmann]

LGTM. +1 for merging.

[tillrohrmann]

@flinkbot approve all