Updates doTestAllowedUids to wait network Lost

doTestAllowedUids did not wait the network disconnect and this made the
test flaky since doTestAllowedUids saw the network from the previous
doTestAllowedUids.
This CL update doTestAllowedUids to wait network Lost

Before this CL, test failed 6 times in 1000 tries.
After this CL, test does not fail in 1000 tries.

Test: atest testAllowedUids --iterations 1000
Bug: 312206245
Change-Id: I270a230c15dfd2c44ba29f203bc55c0f47649e98