Add core-seabase suite to check/gate and use release flavor

traf.yaml change changes all core-regress-* jobs to use release flavor
build.

I have not changed the core-build-nodbg-* job flavor. Since phoenix_quick
still uses debug flavor, both release/debug flavors are covered.

layout.yaml adds core-regress-seabase-* to check/gate pipelines, but
removes it from check-full since that would be redundant.

Jenkins and Zuul changes can be in same commit, since no jenkins jobs
are changing names.

Change-Id: I86909107f138c607972330ee2204f61d2781f347
Merge "Add core-seabase suite to check/gate and use release flavor"