Add a test for getCaptivePortalServerUrl

The API returns a URL that can be used to test the presence of a captive
portal.
The only requirements are that the URL is valid, and HTTP (as per
javadoc).

Bug: 168755498
Test: atest CtsNetTestCasesLatestSdk
Change-Id: I9a92b422a7df2379fadab79ed49b77e7c2fcc393
1 file changed
tree: 0a55d699fd53da92978a332ac589b0f1aeb9c400
  1. tests/