[enh] ./manage node.env - check build tools first

The node.env build environment require npm, ttfautohint and fontforge installed
in the OS.  These tools can be installed by::

    sudo -H ./utils/searx.sh install buildhost

If one of the tools is not installed, the script node.env stops with a
appropriate message.

BTW: We ignore CentOS-7 as developer & build platform

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>