Port #8880 to master Support Cloud testing

[LeeDr]

Support Cloud Kibana testing; Fixes #8861

• tested setting environment variables for all elasticsearch and kibana protocol/host/port/user/pass settings.
• Renamed "TEST_UI__" and "SHIELD__" variables to just be "TEST_*" to make life easier when setting these variables.
• Browsers don't show ports 80 or 443 in the address bar, so filter them out of the expected URL in the navigateToApp function and in the link sharing tests.
• Updated CONTRIBUTING.md to describe how to run tests against some other instance.
• added a try loop around a failed data table test (not really related to Cloud testing but it failed for me once).
• Added 'x-pack' "test" to check for the X-Pack Welcome banner and, if there, opt out, and dismiss. It's in a before method and so doesn't count as a test.
• Instead of looking for the X-Pack welcome banner with some multi-second timeout, I got the outer toaster-container and got the text from it. Getting this and checking if the text contains 'X-Pack' happens in about 0.1s compared to a find timeout for something in the banner with a default of 10s.
• I moved the run:devChromeDriver grunt task from the test:ui:server task to the test:ui:runner task since then you only need to run test:ui:runner against some already running Elasticsearch and Kibana servers.

If anyone wants to run this against my Cloud 5.0 instance I can give you the configuration settings.

This is in the CONTRIBUTING doc as an example for testing against Cloud;

export TEST_KIBANA_PROTOCOL=https
export TEST_KIBANA_HOSTNAME=9249d04b1186b3e7bbe11ea60df4f963.us-east-1.aws.found.io
export TEST_KIBANA_PORT=443
export TEST_KIBANA_USER=elastic
export TEST_KIBANA_PASS=<ping me for this>

export TEST_ES_PROTOCOL=http
export TEST_ES_HOSTNAME=aaa5d22032d76805fcce724ed9d9f5a2.us-east-1.aws.found.io
export TEST_ES_PORT=9200
export TEST_ES_USER=elastic
export TEST_ES_PASS=<ping me for this>
npm run test:ui:runner

[LeeDr]

Selenium tests all passed >> 0/99 tests failed