function replaces the value of a key in the configuration database.
You must specify both the key name and its value, this is because keys are not
unique in the database, so a value is not enough to uniqely identify a key belonging
to a particular parent object.
Strictly, even give the key name and value is not enough to uniquely identify a key,
If there are two (or more) keys with the same name and value, only the first will have
its value changed .
This call returns the CONFDB_OK value if successful, otherwise an error is returned.