Fix e2e test failure when by setting security tenant when visiting Kibana

[tlfeng]

Issue #, if available:
opendistro-for-elasticsearch/opendistro-build#600

The E2E test fails due to the "select your tenant" modal shows up when a user visits Kibana for the first time, and probably because of a change in security plugin in ODFE 1.13.

The modal will disappear if user click any button ("close", "cancel", or "confirm"), or refresh the page.

Description of changes:

• Add security_tenant='private' in the URL parameter of the HTTP request for visiting Kibana.
  The the full request will be like: http://localhost:5601/app/home?security_tenant='private'

Explanation:
From the code in " opendistro-for-elasticsearch/security-kibana-plugin" repository, The security_tenant can be either put in the HTTP request header or the URL parameter.

I chose to put into the URL query parameter, because it didn't work for me to put into the header through Cypress.

According to the document, all users at least have access to 2 tenants: "Private" and "Global". "Private" is the default for "Security Kibana Plugin", so I set it in the test.

Testing:
Started an ODFE cluster through Docker image, and ran yarn run cypress run --env security_enabled=ture

       Spec                                              Tests  Passing  Failing  Pending  Skipped  
  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ ✔  alert_spec.js                            02:23        5        5        -        -        - │
  ├────────────────────────────────────────────────────────────────────────────────────────────────┤
  │ ✔  destination_spec.js                      00:23        4        4        -        -        - │
  ├────────────────────────────────────────────────────────────────────────────────────────────────┤
  │ ✔  monitor_spec.js                          00:28        6        6        -        -        - │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘
    ✔  All specs passed!                        03:15       15       15        -        -        -  

✨  Done in 228.90s.

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[tlfeng]

@skkosuri-amzn Thank you for reviewing the PR so quickly. I realized that I requested the review too early, because I have wrote any description. 😄