[cloud spanner] Add dependency for surefire-junit47

[qian-long]

Fixes junit dependency issue when running tests in a VPC.

[qian-long]

@silverdev, @snehashah16, @nithinsujir, @kolea2 for FYI

[codecov]

Codecov Report

Merging #4526 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #4526 +/- ##
============================================
- Coverage 49.15% 49.15% -0.01% 
Complexity 21934 21934 ============================================
Files 2077 2077 Lines 207174 207174 Branches 24099 24099 ============================================
- Hits 101841 101838 -3 - Misses 97160 97163 +3 
Partials 8173 8173

Impacted Files	Coverage Δ	Complexity Δ
...gle/cloud/storage/testing/RemoteStorageHelper.java	55.28% <0%> (-2.44%)	8% <0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 07ab941...73a4036. Read the comment docs.

[sduskis]

Is this something we should apply for all projects?

[qian-long]

I think this was only missing for spanner. For example, bigtable has a clause for this: https://github.com/googleapis/google-cloud-java/blob/master/google-cloud-clients/google-cloud-bigtable/pom.xml#L134