Clutch::Utils::parse_read_buffer: fix "arg with space" problem

in these methods:

* Clutch::Client#request
* Clutch::Client#request_background
* Clutch::Client#request_multi
* Clutch::Client#request_background_multi

when string with space is passed into arg of job, Clutch::Utils::parse_read_buffer dies.

I fixed this problem.