Comment 0 for bug 1888858

LP: #1885527 raised (not for the first time) a general failure of cloud-init's
documentation to cover 'manual_cache_clean'. In fact, this configuration
value not referenced at all in readthedocs, but only in
doc/examples/cloud-config.txt
  https://github.com/canonical/cloud-init/blob/b70aec8e5ed59298e9fbd5da449350dd3d0002d2/doc/examples/cloud-config.txt#L467

The intent (testing is needed) for manual_cache_clean is:

a.) user-data and system config (/etc/cloud/*.cfg) can set
manual_cache_clean to true or false. As always user-data overrides system
config. vendor-data should also be able to provide the setting.

b.) cloud-init renders /var/lib/cloud/instance/manual-clean
(path_helper.get_ipath_cur("manual_clean_marker")) if

c.) on boot, both ds-identify and cloud-init will check
and respect existance of /var/lib/cloud/instance/manual-clean .
If that file is present, then cloud-init will not make any
attempts to re-discover a metadata service.

So... "unfreeze", if manual_cache_clean was set is just:
 rm -Rf /var/lib/cloud/instance /var/lib/cloud/instance/

I think it would be good to both test that my intent/understanding are
correct, and document it. Also useful might be documenting use case
that makes this necessary which is described in:
  https://bugs.launchpad.net/ubuntu/+source/cloud-init/+bug/1885527/comments/6

Related bugs:
 * bug 1885527: cloud-init regenerating ssh-keys
 * bug 1712680: cloud-init re-generates network config every reboot