Add a bunch of LDAP tests.

    * Adding/removing a user/group/membership with rfc2307(bis) schema.
    * Filtering users/groups with rfc2307(bis) schema.
    * The effect of override_homedir option.
    * The effect of fallback_homedir option.
    * The effect of override_shell option.
    * The effect of shell_fallback option.
    * The effect of default_shell option.
    * The effect of vetoed_shells option.

Fix creation of mixed user/group "member" attribute for RFC2307bis
group entries in ldap_ent.py.

Use a function to generate basic sssd.conf in test_ldap.py to reduce
code duplication.

Split ldap_test.py fixtures into several functions to allow for partial
fixtures and direct use within tests.

Support passing all user attributes to ldap_ent.py's user-creation
functions, in integration tests.

Remove "_rfc2307" from integration test function names for brevity.

Don't use the global LDAP_BASE_DN in integration tests and fixtures, but
instead take it from the LDAP connection object (ldap_conn) passed to
them explicitly. This makes the tests and fixtures a bit more modular.

Previously, only one tab had configured all environment variables
and current working directory was set to source directory.
It's better to open shell in "chroot" directory for troubleshooting purposes.

This patch also open pre-defined tabs with useful
directories with sssd cache, sssd log files, "chroot" directory

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

Reviewed-by: Pavel Reichl <preichl@redhat.com>