Sometimes build fails with error: "worker not pinged". https://ews-build.webkit.org/#/builders/7/builds/365 https://ews-build.webkit.org/#/builders/13/builds/364 https://ews-build.webkit.org/#/builders/9/builds/296 https://ews-build.webkit-uat.org/#/builders/7/builds/474
<rdar://problem/49730598>
Adding "--keepalive 120" in "buildbot-worker create-worker" command seems to fix the issue. Updated https://trac.webkit.org/wiki/EarlyWarningSystem#ConfiguringlocalBuildbotworker accordingly.