test: exclude write-coverage from coverage report

Added a .nyrc configuration file that can be used to configure
test coverage.

Added an exclude rule that removes write-coverage.js from coverage
reports.

Pulled reporter configuration into .nycrc and added an additional
text reporter.

PR-URL: https://github.com/nodejs/node/pull/15194


Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>