Replace the usage of the deprecated wait.Poll() and
wait.PollImmediate() functions with wait.PollUntilContextTimeout().
Since we don't have piping of context around kubeadm,
use context.Background() everywhere.
Some wait.Poll() functions were converted to "immediate" as there
is no point for them to not be. This is done for consistency.
Replace the only instance of wait.JitterUntil with
wait.PollUntilContextTimeout. JitterUntil is not deprecated
but this is also done for consistency.
374e41cf66