when a put request is retried due to the response from registry,
the body of the request should be seekable. A dynamic pipe is added
to the body so that the content of the body can be read again.
Currently a maximum of 5 resets are allowed, above which will fail the
request. A new error ErrReset is introduced which informs that a
reset has occured and request needs to be retried.
also added tests for Copy() and push() to test the new functionality
Signed-off-by: Akhil Mohan <makhil@vmware.com>
8f4c23b69f