Native Image tests are failing when System Properties are used.

[mpeddada1]

Currently some integrations tests that are run with the native profile are resulting in the following errors:

JUnit Vintage:ITSessionPoolIntegrationTest
    ClassSource [className = 'com.google.cloud.spanner.ITSessionPoolIntegrationTest', filePosition = null]
    => java.lang.NullPointerException: Property spanner.testenv.config.class needs to be set
       com.google.cloud.spanner.IntegrationTestEnv.initializeConfig(IntegrationTestEnv.java:68)
       com.google.cloud.spanner.IntegrationTestEnv.before(IntegrationTestEnv.java:77)
       org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:50)
       org.junit.rules.RunRules.evaluate(RunRules.java:20)
       org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
       org.junit.runners.ParentRunner.run(ParentRunner.java:413)
       org.junit.runner.JUnitCore.run(JUnitCore.java:137)
       org.junit.runner.JUnitCore.run(JUnitCore.java:115)
       org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:42)
       org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:80)
       [...]
JUnit Vintage:ITInstanceAdminTest
    ClassSource [className = 'com.google.cloud.spanner.it.ITInstanceAdminTest', filePosition = null]
    => java.lang.NullPointerException: Property spanner.testenv.config.class needs to be set
       com.google.cloud.spanner.IntegrationTestEnv.initializeConfig(IntegrationTestEnv.java:68)
       com.google.cloud.spanner.IntegrationTestEnv.before(IntegrationTestEnv.java:77)
       org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:50)
       org.junit.rules.RunRules.evaluate(RunRules.java:20)
       org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
       org.junit.runners.ParentRunner.run(ParentRunner.java:413)
       org.junit.runner.JUnitCore.run(JUnitCore.java:137)
       org.junit.runner.JUnitCore.run(JUnitCore.java:115)
       org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:42)
       org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:80)
       [...]

This means that system properties are not accessible to the tests after native image compilation. According to the official documentation, System properties are only available at build-time (when the native image builder is building the image) and not at run-time and can't be determined from the maven-surefire/maven-failsafe plugin. This requires us to do a couple of things:

1. Pass the System Property in question directly to the native-image command using -Dspanner.testenv.config.class=.
2. Store the system property's value as the static variable.
3. Initialize the class that is referencing the System Property at build-time. (fix(java): initialize spanner test environment class at build-time and add reflection configurations java-core#734)

Additionally, we also need to specify the system properties to the maven surefire plugin because the native profile uses this plugin to run tests before building the native image.