src,tools: use template literals

Convert string concatenation to template literals. Enforce with lint
rule.

PR-URL: https://github.com/nodejs/node/pull/5778


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>