Summary:
It was found that TestPgDdlConcurrency in ASAN build always fails. When I ran it locally my dev vm became unresponsive.

The test creates 50 threads, which under ASAN build appears to become a resource
hog that caused small test machines to become unresponsive. Because of that, it
affects the entire jenkins test process that attempted to run the test 20 times
before giving up.

I changed the test to use 10 threads for ASAN build so that jenkins test do not
need 20 times of run that all fail. The test now runs under ASAN build, although
a bit flaky now. I will look into how to get rid of the flakiness separately.
Jira: DB-14184

Original commit: 0f389ecaa6ade70cb2849933475920c7ff3f192d / D40204

Test Plan: ./yb_build.sh asan --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 20 --tp 1

Reviewers: kfranz, hsunder

Reviewed By: hsunder

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D40755