* feat: Set which browser to launch via PUPPETEER_PRODUCT
This change introduces a PUPPETEER_PRODUCT environment
variable as a first step toward using Puppeteer with
many different browsers. Setting PUPPETEER_PRODUCT=firefox, for
example, enables Firefox-specific Launcher settings.
The state is also exposed as `puppeteer.product` in the API
to support adding other product-specific behaviour as needed.
The bulk of the change is a refactoring in Launcher
to decouple generic browser start-up from product-specific
configuration.
Respecting the puppeteer-core restriction for PUPPETEER_
environment variables, lazily instantiate the Launcher
based on a `product` Puppeteer.launch option, if available.
* test: Distinguish Juggler unit tests from Firefox
The funit script is renamed to fjunit (j for Juggler, which is
used only by the experimental puppeteer-firefox package.
In contrast, the funit script now refers to running Puppeteer
unit tests against the main puppeteer package with Firefox.
To do so with Firefox Nightly, run:
`BINARY=path/to/firefox npm run funit`
A number of changes in this patch make it easier to run
Puppeteer unit tests in Mozilla's CI.
Don't ignore stdout and stderr when using pipe for remote debugging and dumpio is true. In that case puppeteer process connects to the stdout/stderr streams of the child process and it will not hang.
