Add new e2e test case: initial_pairing_test.

This test verify initial pairing between mainline seeker and
provider simulator. The "pair" is triggered by halfsheet UI.
Test pass if account key device saved on seeker side match
with the one wrote at provider side.

Test: atest -v CtsNearbyMultiDevicesTestSuite
Test: http://recall/-/cycSROwIosTzHgYDSIqPXl/fteYnrnJAwKqYYewUDPUxz
Bug: 214015364
Ignore-AOSP-First: nearby_not_in_aosp_yet
Change-Id: Ida5ba2eea527d1662209a6f60b547398dcdc14e9
13 files changed