Adds rewind function to allow curl seek and retry sending data to server

[jbfitb]

Issue

• Implement CURLOPT_SEEKFUNCTION #1526
• About 1 in 10 Alexa requests fail on mobile devices.
• Requests generally fail with one of two errors: curl error code 56 which is "receive error" or curl error code 65 which is "rewind failed"
• I turned on ACSDK_EMIT_SENSITIVE_LOGS to output curl error messages and me help investigate what was going on
• It looks like the errors (both 56 and 65) are accompanied with this message "necessary data rewind wasn't possible":

CurlEasyHandleWrapper:libcurl:id=AVSEvent-619,text=necessary data rewind wasn't possible
LibcurlHTTP2Request:getResponseCode:responseCode=0
LibcurlHTTP2Connection:streamFinished:streamId=AVSEvent-619,result=Error,CURLcode=56

• It seems that implementing the CURLOPT_SEEKFUNCTION and setting CURLOPT_SEEKDATA will solve this problem
• This is a fairly simple change, as AttachmentReader already has a seek function which mirrors the implementation of CURLOPT_SEEKFUNCTION: Both expect to be able to set the absolute index of the buffer instead of changing the cursor by some delta.

Description of changes:

1. Implemented callback functions for CURLOPT_SEEKFUNCTION
2. Add a rewind function to the read callbacks
3. Call seek on AttachmentReader when called from curl

Testing:

Was able to build and run automated tests. This seems to fix the issue. No more 56 or 65 errors.

[kclchan]

Hi @jbfitb,

Thank you for the pull request. Our process is to make changes internally and run all test before pushing the change to github in the form of a new release. I have added this to our internal tracking system to be assessed and prioritized.

Thanks,
Kenneth