To raise readability when preparing multiple ports in parallel we prefix
also the git clone output with the port name dark-yellow-coloured. To
achieve this we sed the git output. In sed \x1b[ resolves to an escape
sequence and \033[, that we use normally, doesn't. The echo command, at
the other hand, resolves both to an escape sequence. Thus we use the
sed-compatible version in general. This commit inhibits the progress
output of git clone as it can't be redirected to sed.
Ref #1872