Fix flaky CtsHostsideNetworkTests.

'set metered-network' adb command is not blocking, it doesn't
wait for the network to be marked as metered. Updated test
to sleep and poll for metered status.

Bug: 64274313
Test: cts-tradefed run singleCommand cts-dev -m CtsHostsideNetworkTests \
      -t com.android.cts.net.HostsideRestrictBackgroundNetworkTests
Change-Id: Ide3e1633167979bdca912c1c299ad17d988b537e
1 file changed