util: Fix and replace nullvec2str utility function with concatenate()

util: Fix and replace nullvec2str utility function with concatenate()

Multiple issues were found and fixed in previously-unused nullvec2str
function, including major problem with possible stack corruption via
long parameters.

This commit completely rewrites the function to dynamically resize the
buffer while appending new parameters to avoid previous problems.

Additionally, name is changed to somewhat more developer friendly name.

Influenced-by: Mateusz Mościcki and Michał Bloch
Change-Id: Ia97e3851bb4b5779a14704098752e3644c487f0b