OSError exception from host.mkdir() if existing entry and force=True

mkdir will unlink the directory entry found for the path to be created if it exists and force=True, but it never creates the directory.

# touch /tmp/test

# cat > test.py << EOF
from charmhelpers.core import host
host.mkdir('/tmp/test')
host.mkdir('/tmp/test', force=True)
EOF

# python test.py

Well, that's not a real test, but the first call will log "INFO juju-log Making dir /etc/apache2/sites-available root:root 555" but do nothing because the path exists; this is a bit misleading.

The second call with force=True will unlink, not create the dir, and then attempt to chown the non-existent directory which throws and exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/var/lib/juju/agents/unit-ubuntu-repository-cache-0/charm/lib/charmhelpers/core/host.py", line 151, in mkdir
    os.chown(realpath, uid, gid)
OSError: [Errno 2] No such file or directory: '/tmp/test'