SQLMetadata managers do not have retry strategy on polling

[drcrallen]

SQL metadata mangers do not have a smart retry strategy when they are polling their databases. A retry strategy should retry (with backoff) on acute errors and emit an alert if the retries fail.

This conversation came up in #1366

Currently the managers simply skip that polling period and try again the next time around.

[gianm]

Would wrapping the calls in something like SQLMetadataStorageActionHandler.retryingHandle work? (It would have to be made into a static I suppose)

Fwiw, I just noticed that Postgres doesn't have a reasonable implementation of isTransientException, and filed #1382 for that.

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