[PATCH 1 of 5] commandserver: add _readstr and _readlist

[Jun Wu]

On 02/16/2016 02:02 PM, Yuya Nishihara wrote:
> Nit: I prefer '' than None because length == 0 can be a valid string.
> And it will make _readlist() shorter.

Yes, return '' is more correct, will do the change. But _readlist()
won't be shorter since ''.split('\0') is [''], not [].