Configuration read and write need to be symmetric

If I query the configuration with `iovnscli` or the REST API I get `*_period` parameters in nanoseconds.  When I try to update the configuration I have to specify periods as durations.  That mismatch in time formats is a real pain since I have to specify all configuration parameters even if I just want to update one.

`*_period` flags for `iovnscli` should be in nanoseconds.