samdb: use int for get and set methods instead of digit str

samdb: use int for get and set methods instead of digit str

This will make the API work in a nature way.

Also, because of a defect in ldb API, code like `res[0]["maxPwdAge"][0]`
will return bytes even in Python3, which will cause trouble. By casting
the value to int, we avoid the str/bytes issue.

Signed-off-by: Joe Guo <joeg@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>