Update vm_allocation_manager.py

Problem COnfirmed: i was checking the link ratio, but has long has the switch ratio was not above the maximum, it still accepts this switch has being ok.

You can see below in bold the values:
"DEBUG:VM.vm_allocation_manager:DPID = 5, Port = 3, Link ratio = 1.10185084301((0.0185084300823+11)/10.0)  - Getting Link Ratio... DONE
DEBUG:VM.vm_allocation_manager:DPID = 5, Ratio = 0.642980279963 - Getting switch ratio... DONE"

Quick fix was released