16029: Adds support for reading YAML fixtures and receive config data.

16029: Adds support for reading YAML fixtures and receive config data.

Also, adds a command to reset the testing database.
Config data can be passed in several ways:

* Running 'yarn run cypress [open|run] --env fixtures=/a/path,controller_url=...'
* Setting environment variables named with the 'CYPRESS_' prefix.
* Using Cypress.config() inside the test cases.

For now, 3 config items are needed:

1. Arvados fixtures path
2. System root token (defined on arvados-boot's zzzzz.yml config file) so a
   database reset can be called.
3. Controller's URL

Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <lucas@di-pentima.com.ar>