fix: plain text when testing emulator connection

[thiagotnunes]

Uses plain text, instead of ssl when testing for local connections. This fixes connection checks when using the MockSpannerServiceImpl and it works with the emulator as well.

Without this fix we would get a transport error when testing the getConnection when using the MockSpannerServiceImpl, since the client would expect TLS, while the server would be serving plainText.

[codecov]

Codecov Report

Merging #1020 (f43896f) into master (25890de) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@ Coverage Diff @@ ## master #1020 +/- ## ============================================ - Coverage 85.12% 85.10% -0.02%  + Complexity 2627 2623 -4  ============================================ Files 155 155 Lines 14369 14374 +5 Branches 1340 1340 ============================================ + Hits 12231 12233 +2  - Misses 1571 1573 +2  - Partials 567 568 +1 

Impacted Files	Coverage Δ	Complexity Δ
...oud/spanner/connection/LocalConnectionChecker.java	82.05% <100.00%> (+8.52%)	6.00 <1.00> (+1.00)
.../google/cloud/spanner/AbstractLazyInitializer.java	92.85% <0.00%> (-7.15%)	4.00% <0.00%> (-1.00%)
...ain/java/com/google/cloud/spanner/SessionPool.java	88.93% <0.00%> (-0.39%)	71.00% <0.00%> (-2.00%)
...a/com/google/cloud/spanner/SessionPoolOptions.java	69.53% <0.00%> (ø)	17.00% <0.00%> (-1.00%)

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[olavloite]

Thanks for noticing that one!