Fix testWifiConfigLockdown failure due to wifi not being ready

This test case will add a network before wifi is ready. Thus, adding
network will be fail and test case will not pass.

For normal use (eg. WifiManagerTest.java), when a test case need to use
wifi, it will listen to wifi state change broadcasts or sleep a while to
make sure wifi is enabled. For some chips, enabling wifi takes about 2
seconds.  enable wifi. Running this test case in these chips may cause
the same issue.

Solution: After enabling wifi, sleep a while make sure wifi is enabled.

Bug: 25171253
Change-Id: I0fa28db34ad59d2a0f1340d4602363a3ab1713f2
3 files changed