CloudStorageReadChannel: more detailed error messages when retries/reopens are exhausted

[droazen]

Include the maxChannelReopens/maxRetries in the exception messages thrown
when reopens/retries are exhausted in CloudStorageReadChannel

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[droazen]

The bot seems not to know about the CLA between my organization (https://www.broadinstitute.org/) and Google. I'll try to fix this, but in the mean time @jean-philippe-martin perhaps you could take over this change and re-submit it yourself in the interests of getting it in?

[coveralls]

Coverage increased (+0.008%) to 81.162% when pulling fb22ea7 on droazen:dr_better_CloudStorageReadChannel_error_messages into 19262b7 on GoogleCloudPlatform:master.

[jean-philippe-martin]

@droazen done, #2219

[droazen]

Thanks @jean-philippe-martin ! Closing this in favor of #2219