Update test code to match new iptables behaviour.

iptables is changing the locking code from binding to an abstract
UNIX socket to calling flock() on a real file. Update test code
that acquires the iptables lock.

Also, make said code more robust by retrying up to 10 times if
the lock is held. This should make the test less flaky.

Bug: 36108349
Test: IptablesRestoreControllerTest passes with new iptables
Change-Id: I1d1d454d78382e76d178c4ef43f2c40a46f81f62