Configurable Retry Policy

[joe-maley]

Both class blob_client constructors initialize executor_context blob_client::m_context with the default class retry_policy. The default retry policy retries 26 times with an exponential back-off up to 60 seconds on each retry.

Please support a configurable retry policy. I'd suggest:

1. Allow class retry_policy to be constructed with both a maximum retry count and a retry interval.
2. Allow class blob_client to be constructed with an instance of class retry_policy.

[Jinming-Hu]

@joe-maley Yes, you're right. The existing retry policy doesn't make too much sense. We also have other customers complaining about this, and also have pending PR #54 trying to fix this problem. We'll consider adding this feature in future release. Thanks for your feedback.

[Jinming-Hu]

We added configurable retry policy in latest 0.3.0 release. The default retry count is also changed from 25 to 3.