python/samba/tests: don't lower case path names in connect_samdb()

python/samba/tests: don't lower case path names in connect_samdb()

We should not lower case file names, because we may get a path to sam.ldb.
Now we only lower case ldap urls.

For a long time I got failing private autobuild like this:

[1623(9233)/1718 at 1h28m9s] samba4.urgent_replication.python(dc)(dc:local)
Failed to connect to ldap URL
'ldap:///memdisk/metze/w/b12985/samba/bin/ab/dc/private/sam.ldb' - LDAP client
internal error: NT_STATUS_NO_MEMORY
Failed to connect to
'ldap:///memdisk/metze/w/b12985/samba/bin/ab/dc/private/sam.ldb' with backend
'ldap': (null)
UNEXPECTED(error):
samba4.urgent_replication.python(dc).__main__.UrgentReplicationTests.test_attributeSchema_object(dc:local)
REASON: _StringException: _StringException: Content-Type:
text/x-traceback;charset=utf8,language=python
traceback
322

The problem is that /memdisk/metze/W/ is my test directory instead
of /memdisk/metze/w/.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11804

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jelmer Vernooij <jelmer@samba.org>
(cherry picked from commit 0e37189dab01a80c10143a54b80859229e181e9b)