manager: change default timeout from 10s to 60s (#1827)
manager: change default timeout from 10s to 60s (#1827)

Summary:
When running on Google-internal Colab, launching a fresh TensorBoard
instance usually takes around 12 seconds. (It’s faster on public Colab.)
Setting the timeout to 60s should do the trick.

This commit updates the default timeout so that users don’t have to run
the `%tensorboard` magic twice (once for it to start and time out, and
once for it to pick up the now-existing instance).

Test Plan:
I made the analogous change inside google3, and `%tensorboard` worked on
the first try; it’s never worked without timing out before.

wchargin-branch: manager-20s

tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard