Add unit tests for cmd/house_keeping
Add unit tests for cmd/house_keeping

So far we don't have unit tests for method house_keeping_db_cleanup,
,spare_amphora_check and main in file cmd/house_keeping.py,
this patch is to add unit tests for these 3 methods.

Change-Id: I2f45b905d96a883b364e7645eeac0a7b8a1e9aba

openstack/octavia,openstack/octavia,openstack/octavia