Tests - ability to run against an existing tenant

[elv-serban]

OVERVIEW

Initial tests used to create a new admin group (which was used to identify the tenant) and provision the new tenant.
Newer changes create an actual tenant and its tenant admin and content admin groups.

Add a TestConfiguration option to specify an existing tenant, instead of creating a new one.

Also:

• if a tenant is specified in TestConfiguration - check that PRIVATE_KEY is the tenant root key
• reduce the funds for each test (from 2 to maybe 0.2 if it works)

This should replace the tenant_admin branch which is used to avoid creating and provisioning a new tenant with each test run.