WiFiRvR: group test cases into a suite.

 - update control.wifirvr based on wiley's example (control.wifi_matfunc)
 - fix one import error in network_WiFi_RateRange.py

BUG=chromium:267889
TEST=Manual (run_remote_tests.sh <blah> suite:wifirvr)

Change-Id: I1bfff55157d8995bc5dfdc94ab7b5af5f5be403b
Reviewed-on: https://gerrit.chromium.org/gerrit/64412
Reviewed-by: Scott Zawalski <scottz@chromium.org>
Commit-Queue: Tan Gao <tgao@chromium.org>
Tested-by: Tan Gao <tgao@chromium.org>
12 files changed