Added retry mechanism for isCapped check

[dushyantbangal]

Please note: When the database is taken down at

handleCursorClosed -> We're now ready. Poll
checkCappedAndPoll
checkCappedAndPoll -> Cannot stat isCapped. Retry
checkCappedAndPoll

and restarted after a minute or so, nothing happens.

This also happens my in your

handleCursorClosed -> Wait for the database to be connected

I think it keeps waiting for the mongodb to reply, but doesn't get any timeout error from mongodb driver.

[coveralls]

Coverage decreased (-0.5%) to 92.397% when pulling 59e59d5 on dushyantbangal:master into bc72263 on mcollina:master.