[SPARK-28701][INFRA][FOLLOWUP] Fix the key error when looking in os.environ

[shaneknapp]

What changes were proposed in this pull request?

i broke run-tests.py for non-PRB builds in this PR:
#25423

Why are the changes needed?

to fix what i broke

Does this PR introduce any user-facing change?

no

How was this patch tested?

the build system will test this

[shaneknapp]

@HyukjinKwon @srowen

it behooves us, when checking for env vars in non-prb builds, to always check for the key before referencing it in an if statement. :)

[srowen]

Oops, right.

[shaneknapp]

once we get to the Running Spark unit tests block i will feel comfortable in merging this...

[shaneknapp]

thanks @dongjoon-hyun

[dongjoon-hyun]

+1, LGTM.

[SparkQA]

Test build #109747 has finished for PR 25585 at commit 9b6fc4f.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[shaneknapp]

• This patch fails Spark unit tests.

this has to be unrelated... should i test again or just go ahead and merge?

[srowen]

It clearly fixes the issue that was failing before, right? you can see the desired output in the logs that even starts the tests? then I'd merge it. That can't be related.

[shaneknapp]

alrighty! things looking good. the builds i broke (spark-master-test-sbt-*) are good, and i spot-checked one (https://amplab.cs.berkeley.edu/jenkins/job/spark-master-test-sbt-hadoop-3.2/324/) and the spark unit tests just started successfully:

========================================================================
Running Spark unit tests
========================================================================
[info] Running Spark tests using SBT with these arguments:  -Phadoop-3.2 -Pkubernetes -Phadoop-cloud -Phive -Phive-thriftserver -Pyarn -Pspark-ganglia-lgpl -Pkinesis-asl -Pmesos test
Using /usr/java/jdk1.8.0_191 as default JAVA_HOME.
Note, this will be overridden by -java-home if it is set.