Fix: logutil: pipe: Do not depend on snprintf() return value for calculations

Fix: logutil: pipe: Do not depend on snprintf() return value for calculations

snprintf() can return numers of characters that "would have been
written if buffer would be large enough", not actual characters
written.

This commits reworks logger request command construction to
avoid snprintf().

Problem pointed out by 김원영 <won0.kim@samsung.com> (thank you!)

Change-Id: I664cc0ce779eaff3c004e47fd5102b0576295630