Ignore testReevaluateNetwork until Q

The method did not exist until Q, so the test is not relevant on such
devices.

Test: atest CtsNetTestCasesLatestSdk:android.net.CaptivePortalTest on Q
          and R devices
Bug: 150918852
Merged-In: I913b6eaa61bfd4f1964b324dcb4dd272aa8cc583
(cherry picked from commit 4d166d7b)

Change-Id: I2ddeee53d4ef63f01b791e3e95161194e29d3978