MAR-218: Fix the custom m_ldap_permissions module to work correctly with ansible-lint:

- In order for things to behave correctly, module should not invoke
the main part of code automatically during import, but only if run
via CLI.
- Without this the ansible-lint kept erroring out with:

"missing required arguments: filter, rules"

MAR-218: Fix execution of the LDAP database permissions module:

- Python interpreter path must be specified explicitly (without the
env wrapper).

MAR-125: Eliminated a couple of warnings:

- Use the file module when cleaning-up the /etc/duply/main/gnupg directory.
- Mark the bind_password in m_ldap_entry and m_ldap_permissions as no_log
parameters.

MAR-117: Renamed ldap_entry and ldap_permissions modules:

- Renamed ldap_entry module to m_ldap_entry.
- Renamed ldap_permissions module to m_ldap_permissions.
- Renames done to avoid collisions with official modules (at least for
ldap_entry).