CtsVerifier: fixes new wifi tests for headless system user mode.

- DISALLOW_ADD_WIFI_CONFIG must be applied to the device owner
- DpmWrapper needs to mock setMinimumRequiredWifiSecurityLevel()
  and setWifiSsidPolicy()

Test: manual verification

Fixes: 231906839
Fixes: 231907861
Fixes: 231908502

Ignore-AOSP-First: contains new DPM API added on Android T

Change-Id: I4d17ab3e23ec5fdba2b253f1869687e656bc378c
2 files changed