Add ability to change keepalive value (#338)

Use an environment variable, `BUILD_WORKER_KEEPALIVE`, to control the keepalive value set in the `buildbot.tac` file. Defaults to `240` which seemed to prevent disconnects of the worker in webkit infrastructure.

Author: donny-dont

buildbot-worker/BuildbotWorker/Run-BuildbotWorker.ps1

@@ -34,6 +34,7 @@ Write-Host 'Buildbot information';
 Write-Host ('Name: {0}' -f $env:BUILD_WORKER_NAME);
 Write-Host ('Admin: {0} <{1}>' -f $env:ADMIN_NAME,$env:ADMIN_EMAIL);
 Write-Host ('Description: {0}' -f $env:HOST_DESCRIPTION);
+Write-Host ('Keep-alive: {0}' -f $env:BUILD_WORKER_KEEPALIVE);
 
 # Print the host information
 $cs = Get-WmiObject -Class Win32_ComputerSystem;

buildbot-worker/BuildbotWorker/buildbot.py

@@ -12,6 +12,7 @@ def _get_options():
         'port': os.environ.get('BUILD_HOST_PORT', '17000'),
         'worker': os.environ.get('BUILD_WORKER_NAME'),
         'password': os.environ.get('BUILD_WORKER_PASSWORD'),
+        'keepalive': os.environ.get('BUILD_WORKER_KEEPALIVE', '240'),
         # info/admin
         'name': os.environ.get('ADMIN_NAME'),
         'email': os.environ.get('ADMIN_EMAIL'),

buildbot-worker/BuildbotWorker/buildbot.tac.tmpl

@@ -26,7 +26,7 @@ buildmaster_host = '$host'
 port = $port
 workername = '$worker'
 passwd = '$password'
-keepalive = 600
+keepalive = $keepalive
 umask = 0o022
 maxdelay = 300
 numcpus = None