rt-unit: Replace hard-coded strings with constants
rt-unit: Replace hard-coded strings with constants

The test_tracker.py file over time had had the host and
hypervisor_hostname (nodename) values hard-coded as strings throughout
the file. This commit simply replaces those strings with references to
module-level constants in order to simplify and make the test cases more
consistent. Some of the test cases were using the string 'fake-host' to
refer to the host and 'fakehost' to refer to the nodename. Other tests
were using the string 'fake-node' to refer to the nodename. This fixes
those all up to be consistent and refer to two constants.

Change-Id: I4158f5661cf083e224171ff47103f77a79a94125

sebrandon1/nova,sebrandon1/nova,klmitch/nova,rajalokan/nova,vmturbo/nova,rajalokan/nova,hanlind/nova,mahak/nova,vmturbo/nova,mahak/nova,cloudbase/nova,mikalstill/nova,rajalokan/nova,Juniper/nova,gooddata/openstack-nova,phenoxim/nova,rahulunair/nova,klmitch/nova,openstack/nova,rajalokan/nova,klmitch/nova,mikalstill/nova,sebrandon1/nova,rahulunair/nova,bigswitch/nova,openstack/nova,cloudbase/nova,jianghuaw/nova,jianghuaw/nova,jianghuaw/nova,bigswitch/nova,alaski/nova,mahak/nova,klmitch/nova,gooddata/openstack-nova,openstack/nova,hanlind/nova,phenoxim/nova,vmturbo/nova,cloudbase/nova,vmturbo/nova,Juniper/nova,Juniper/nova,rahulunair/nova,gooddata/openstack-nova,alaski/nova,gooddata/openstack-nova,Juniper/nova,jianghuaw/nova,mikalstill/nova,hanlind/nova