Make the size of the build node HDD configurable

Fixes #1520

buildman/manager/executor.py

@@ -75,6 +75,7 @@ class BuilderExecutor(object):
         coreos_channel=coreos_channel,
         worker_tag=self.executor_config['WORKER_TAG'],
         logentries_token=self.executor_config.get('LOGENTRIES_TOKEN', None),
+        volume_size=self.executor_config.get('VOLUME_SIZE', '42G'),
     )
 
 
@@ -119,7 +120,7 @@ class EC2Executor(BuilderExecutor):
     ec2_conn = self._get_conn()
 
     ssd_root_ebs = boto.ec2.blockdevicemapping.BlockDeviceType(
-        size=48,
+        size=int(self.executor_config.get('BLOCK_DEVICE_SIZE', 48)),
         volume_type='gp2',
         delete_on_termination=True,
     )

buildman/templates/cloudconfig.yaml

@@ -61,7 +61,7 @@ coreos:
         ConditionPathExists=!/var/lib/docker.btrfs
         [Service]
         Type=oneshot
-        ExecStart=/usr/bin/truncate --size=42G /var/lib/docker.btrfs
+        ExecStart=/usr/bin/truncate --size={{ volume_size }} /var/lib/docker.btrfs
         ExecStart=/usr/sbin/mkfs.btrfs /var/lib/docker.btrfs
     - name: var-lib-docker.mount
       enable: true