Iterpolation of value in set method for SSSDConf class

[x00Pavel]

When the values contain percent sign (e.g. %20 as the encoding of space), it's not correctly inserted into the file so. Single percent would cause an exception, doubling (as suggested in the official doc) of the percent sign still leads to wrong interpolation.

Suggestion

For SSSDConf use python3-sssdconfig module that is shipped with sssd package.