Allow useage of server IDs as well as names.

RAX have some hidden images useful for build a xenserver host.
Ensure nodepool can use these by referring to them by image UUID.

Change-Id: Idfefc60e762740f4cffa437933007942a0920970
Make jenkins get info task synchronous

This is called within the main loop which means if there are a lot
of jenkins tasks pending, the main loop waits until they are all
finished.  Instead, make this synchronous.  It should be lightweight
so the additional load on jenkins should be negligible.

Also increase the sleep in the main loop to 10 seconds to mitigate
this somewhat.

Change-Id: I16e27fbd9bfef0617e35df08f4fd17bc2ead67b0
Merge "Allow useage of server IDs as well as names."