Description of problem:
Deployed 1 controller, 1 compute, 1 ceph configuration with GnocchiBackend: file. Changed default backend dir from /var/lib/gnocchi to /var/lib/test, in gnocchi_metricd tried to create new dir /var/lib/test: permission denied.

Version-Release number of selected component (if applicable):
gnocchi-common-4.3.3-0.20181005084758.54bae4e.el7ost.noarch
python-gnocchi-4.3.3-0.20181005084758.54bae4e.el7ost.noarch
puppet-gnocchi-13.3.1-0.20181013121920.4b95b4b.el7ost.noarch
gnocchi-metricd-4.3.3-0.20181005084758.54bae4e.el7ost.noarch
python2-gnocchiclient-7.0.4-0.20180823073245.64814b9.el7ost.noarch

How reproducible:
100%

Steps to Reproduce:
1. Deploy 1 controller, 1 compute, 1 ceph with an additional parameter GnocchiBackend: file.

2. Test that the measures are shown after deployment: create a new instance, watch cpu measures, observe that the directories are created on /var/lib/gnocchi in gnocchi_api container.

3. In /var/lib/config-data/puppet-generated/gnocchi/etc/gnocchi/gnocchi.conf change file_basepath=/var/lib/test. Restart gnocchi_metricd container. Verify that the config /etc/gnocchi/gnocchi.conf is changed in gnocchi_metricd container.

4. In gnocchi_metricd container try to add a folder test under /var/log. Get error "permission denied". Cannot create the folder.

Note: when trying to add "test" folder under /var/lib/ in gnocchi_api container, everything works ok - the folder is created, the permissions can be changed.

Actual results:
Permission is denied

Expected results:
New folder is created

Additional info:
[heat-admin@controller-0 ~]$ tail /var/log/containers/gnocchi/gnocchi-metricd.log
    self._build_metric_path(metric, aggregation),
  File "/usr/lib/python2.7/site-packages/gnocchi/storage/file.py", line 136, in _build_metric_path
    return os.path.join(self._build_metric_dir(metric),
  File "/usr/lib/python2.7/site-packages/gnocchi/storage/file.py", line 121, in _build_metric_dir
    if self.SUBDIR_LEN > 0:
  File "/usr/lib/python2.7/site-packages/gnocchi/storage/file.py", line 76, in SUBDIR_LEN
    elif self.is_old_directory_structure():
  File "/usr/lib/python2.7/site-packages/gnocchi/storage/file.py", line 98, in is_old_directory_structure
    for p in os.listdir(self.basepath):
OSError: [Errno 2] No such file or directory: '/var/lib/test'