Add a sync.Mutex to guard the append to RecordedWaitOptions in
GetWaiterWithOptions, fixing a data race detected by -race when
concurrent goroutines (e.g. upgrade + rollback) both call
GetWaiterWithOptions on the same FailingKubeClient instance.
Fixes race failures in TestUpgradeRelease_Interrupted_RollbackOnFailure
and TestInstallRelease_RollbackOnFailure_Interrupted.
Signed-off-by: Terry Howe <thowe@nvidia.com>