tests: Make pmksa_cache_opportunistic_connect more robust

This test case could fail if the cfg80211 scan cache brought in a BSS
entry from an earlier test case and a new scan did not get executed
prior to the ROAM command. Fix this by forcing the scan to go through
prior to roaming to AP2

This issue showed up with the following test case sequence:
connect_cmd_roam pmksa_cache_opportunistic_connect

Signed-off-by: Jouni Malinen <j@w1.fi>

tests/hwsim/test_pmksa_cache.py

@@ -249,7 +249,7 @@ def test_pmksa_cache_opportunistic_connect(dev, apdev):
 
     wpas.dump_monitor()
     logger.info("Roam to AP2")
-    wpas.scan_for_bss(bssid2, freq="2412")
+    wpas.scan_for_bss(bssid2, freq="2412", force_scan=True)
     wpas.request("ROAM " + bssid2)
     ev = wpas.wait_event(["CTRL-EVENT-EAP-STARTED",
                             "CTRL-EVENT-CONNECTED"], timeout=10)