Move read/write handles in VMware drivers to OSLO

There is lot of common code between VMware drivers for nova and cinder;
for e.g., session management and VIM API invocation code. The new
VMware driver for glance and the telemetry agent for vSphere are also
planning to use this common code. This change moves the classes defining
read and write handles for image transfer between VMware servers and
image service into OSLO.

Change-Id: I05bdda82c5393049726647a1ba5e38c2c0add72d
Implements: blueprint vmware-api