Let OS choose free port in MembershipKeyTest. Bug: 293982420 Test: CtsLibcoreTestCases Change-Id: I31143ca85dd0ddc3ae47915f1741f24d39dec3c8 Merged-In: I31143ca85dd0ddc3ae47915f1741f24d39dec3c8 (cherry picked from commit 532038b985234d28f4b34c7b66289c18c9427391)