Delegate directive value quoting/unquoting to separate functions
Separate functions were added to installutils module to quote/unquote a
string in arbitrary characters.
`installutils.get/set_directive` functions will use them to enclose
the directive values in double quotes/strip the double quotes from
retrieved values to maintain the original behavior.
These functions can be used also for custom quoting/unquoting of
retrieved values when desired.
https://fedorahosted.org/freeipa/ticket/6460
Reviewed-By: Tomas Krizek <tkrizek@redhat.com>
Reviewed-By: Petr Spacek <pspacek@redhat.com>