ci(bigtable): allow bulkTests profile to skip unit tests by removing explicit skipTests override (#13906)

The normal CI units is running the BigTable tests even though bigtable
has their own split-units config.

This seems to stem from bulkTest profile having the skipTests property
be overwritten by BigTable's default config. This change updates it so
that bulkTests profile can properly skip BigTable tests when enabled.
When the profile is not enabled, the skipTests property defaults to `""`
which is evaluated to false by default.

Author: lqiu96

java-bigtable/google-cloud-bigtable/pom.xml

@@ -20,8 +20,9 @@
     <site.installationModule>google-cloud-bigtable</site.installationModule>
 
     <!-- Enable the ability to skip unit tests and only run integration tests,
-         while still respecting global skipTests override. -->
-    <skipTests>false</skipTests>
+         while still respecting global skipTests override and parent bulkTests profile.
+         Do NOT set an explicit <skipTests>false</skipTests> here, as submodule property
+         declarations override parent profile settings and prevent -PbulkTests from working. -->
     <skipUnitTests>${skipTests}</skipUnitTests>
     <skipITs>${skipTests}</skipITs>
     <!-- Configure test logging output. By default tests print info logs to stdout/err.