vmware: Force chunked transfer for upload-to-image

The upload-to-image operation downloads (using stream-optimized HTTP NFC
transfer) the virtual disk corresponding to the volume to a pipe from
where the glance image client reads the data for upload. Due to a recent
change in the glance image client, success in seeking the input file
object results in forgoing the chunked transfer in favor of regular
transfer. The glance image client expects an IOError if the input file
object is a pipe. Currently the pipe seek() is a NOP and this results in
upload-to-image failure. This changes fixes such failures by throwing
an IOError indicating an illegal seek.

Change-Id: I2e69fc4103559d49d2cee16ea04787a252dbf879
Closes-Bug: #1295239