Add option to set temp upload dir for image upload

The default Django location for file uploads including new Glance
images is /tmp, this adds an optional configuration parameter to set
this to another location which could be a separate filesystem if
needs be.

Change-Id: Ifd5a56fe08f39d72ecdc8d9e2b4976b0dbc87c54
Merge "Add option to set temp upload dir for image upload"