Deploying CentOS images fails with AttributeError: module 'curtin.util' has no attribute 'RunInChroot'

After updating to 2.1.0~alpha3+bzr5368-0ubuntu1~16.04.1, CentOS 6 and CentOS 7 images fail to deploy. From the installation output:

CentOS 6:

Traceback (most recent call last):
  File "/tmp/tmpgke7jc8_/target/curtin/curtin-hooks.py", line 342, in <module> main()
  File "/tmp/tmpgke7jc8_/target/curtin/curtin-hooks.py", line 333, in main
  grub_root = get_grub_root(target)
  File "/tmp/tmpgke7jc8_/target/curtin/curtin-hooks.py", line 181, in get_grub_root
  with util.RunInChroot(target) as in_chroot:
AttributeError: module 'curtin.util' has no attribute 'RunInChroot'

CentOS 7:

Traceback (most recent call last):
  File "/tmp/tmp9mnktq4v/target/curtin/curtin-hooks.py", line 332, in <module> main()
  File "/tmp/tmp9mnktq4v/target/curtin/curtin-hooks.py", line 316, in main
  grub2_mkconfig(target)
  File "/tmp/tmp9mnktq4v/target/curtin/curtin-hooks.py", line 151, in grub2_mkconfig
  with util.RunInChroot(target) as in_chroot:
AttributeError: module 'curtin.util' has no attribute 'RunInChroot'