test: Apply currently set wait timeout to waitPageLoad()

Commit 49ee017 set a static 15s timeout for the waitPageLoad()
helper, but some tests like `TestIPA.testClientCertAuthentication`
require a longer one.

So support a `timeout=` option, and fall back to 15s if it is not set.
In Browser.open(), pass the currently set timeout in the CDP driver
(i.e. from `Browser.wait_timeout())`.

test/common/chromium-cdp-driver.js

@@ -227,7 +227,7 @@ function setupLocalFunctions(client) {
         const timeout = setTimeout(() => {
             pageLoadHandler = null;
             reject("Timeout waiting for page load"); // eslint-disable-line prefer-promise-reject-errors
-        }, 15000);
+        }, (args.timeout ?? 15) * 1000);
         pageLoadHandler = () => {
             clearTimeout(timeout);
             pageLoadHandler = null;

test/common/testlib.py

@@ -242,7 +242,7 @@ def open(self, href: str, cookie: Optional[Dict[str, str]] = None, tls: bool = F
             # But that option has the inverse effect with Chromium (argh)
             opts["transitionType"] = "reload"
         self.cdp.invoke("Page.navigate", url=href, **opts)
-        self.cdp.invoke("waitPageLoad")
+        self.cdp.invoke("waitPageLoad", timeout=self.cdp.timeout)
 
     def set_user_agent(self, ua: str):
         """Set the user agent of the browser