[TS-3085] Large POSTs over (relatively) slower connections failing in ats5
Call ERR_get_error_line_data() via SSL_CLR_ERR_INCR_DYN_STAT to clean up
the error queue after processing an SSL_ERROR_SSL. Also, added consistent
wrappers to SSL I/O functions and removed errno based looping on SSL_Write
per James Peach's recommendations.  Note that, this change removes the apparent
logic of reattempting SSL_Write on transient error cases (such as ENOBUF), since
openSSL documentation doesn't indicate that errno is set during SSL_Write.
https://www.openssl.org/docs/ssl/SSL_write.html