WaitForRunning risks a race condition where the allocation succeeds and
completes before WaitForRunning is called (or while it is running).
Here, I made the behavior match the function documentation.
I considered making it stricter, but callers need to account for
allocation terminating immediately after WaitForRunning terminates
anyway.
Although the really exciting change is making WaitForRunning return the
allocations that it started. This should cut down test boilerplate
significantly.
Not setting the host name led the Go HTTP client to expect a certificate
with a DNS-resolvable name. Since Nomad uses `${role}.${region}.nomad`
names ephemeral dir migrations were broken when TLS was enabled.
Added an e2e test to ensure this doesn't break again as it's very
difficult to test and the TLS configuration is very easy to get wrong.
This drops the testings stdlib pkg from our dependencies. Saves a
whopping 46kb on our binary (was really hoping for more of a win there),
but also avoids potential ugliness with how testing sets flags.
