Merge pull request #19 from Metaswitch/ut_fix

Re-add variables to settings.py in order to fix UT failures
HSS_HOSTNAME should be HSS_IP
Merge pull request #20 from Metaswitch/hss_hostname_var_rename

HSS_HOSTNAME should be HSS_IP
Sensible default values for HSS/password encryption settings when using an /etc/clearwater/config without the values set
Deprecate HSS_ENABLED in favour of checking whether HSS_IP is blank or 0.0.0.0
Remove remaining references to HSS_ENABLED
Merge branch 'sensible_defaults' into ut_fix

Conflicts:
	src/metaswitch/crest/settings.py
	src/metaswitch/crest/test/api/homestead/credentials.py
	src/metaswitch/crest/test/api/homestead/filtercriteria.py
	src/metaswitch/crest/test/api/homestead/hss/gateway.py