Looking at our graphs, we're still spiking up into the 30-60
concurrent building range at times, which seems to result in some
launches exceeding the already lengthy timeout and wasting quota,
but when things do manage to boot we effectively utilize most of
max-servers nicely. The variability is because max-concurrency is
the maximum number of in-flight node requests the launcher will
accept for a provider, but the number of nodes in a request can be
quite large sometimes.
Raise max-servers back to its earlier value reflecting our available
quota in this provider, but halve the max-concurrency so we don't
try to boot so many at a time.
Change-Id: I683cdf92edeacd7ccf7b550c5bf906e75dfc90e8