Description of problem:
$ mock -r ruby ruby-2.3.0-0.5.r51856.fc24.src.rpm 
INFO: mock.py version 1.2.13 starting (python version = 3.4.3)...
Start: init plugins
INFO: selinux disabled
Finish: init plugins
Start: run
INFO: Start(ruby-2.3.0-0.5.r51856.fc24.src.rpm)  Config(ruby)
Start: clean chroot
ERROR: Exception(ruby-2.3.0-0.5.r51856.fc24.src.rpm) Config(ruby) 0 minutes 0 seconds
INFO: Results and/or logs in: /var/lib/mock/ruby/result
ERROR: 'str' does not support the buffer interface
Traceback (most recent call last):
  File "/usr/sbin/mock", line 649, in main
    run_command(options, args, config_opts, commands, buildroot, state)
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/sbin/mock", line 729, in run_command
    do_rebuild(config_opts, commands, buildroot, args)
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/sbin/mock", line 495, in do_rebuild
    post=post_build, clean=clean)
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/sbin/mock", line 438, in rebuild_generic
    commands.clean()
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.4/site-packages/mockbuild/backend.py", line 72, in clean
    self.buildroot.delete()
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.4/site-packages/mockbuild/buildroot.py", line 556, in delete
    util.orphansKill(p)
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.4/site-packages/mockbuild/util.py", line 186, in orphansKill
    for name in vm_list.split("\n"):
TypeError: 'str' does not support the buffer interface

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/sbin/mock", line 833, in <module>
    main()
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/sbin/mock", line 651, in main
    buildroot.finalize()
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.4/site-packages/mockbuild/buildroot.py", line 540, in finalize
    util.orphansKill(self.make_chroot_path())
  File "/usr/lib/python3.4/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/lib/python3.4/site-packages/mockbuild/util.py", line 186, in orphansKill
    for name in vm_list.split("\n"):
TypeError: 'str' does not support the buffer interface



Version-Release number of selected component (if applicable):
$ rpm -q mock
mock-1.2.13-2.fc24.noarch


How reproducible:


Steps to Reproduce:
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Actual results:


Expected results:


Additional info:
This seems to be Python3 incompatibility introduced by bug 1171737. I can use --old-chroot as a workaround.