Add swift config option to service_available group

This commit adds a new config option, swift, to the service_available
group. This option can be used to specify whether swift is running.
It also adds a skip to the base object test class, replacing the
endpoint detection skip.

Change-Id: I8d81071cf5077fb880f04c04b330b1f4132a58f0
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 435bb6c..32fe484 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -354,3 +354,5 @@
 neutron = false
 # Whether or not glance is expected to be available
 glance = True
+# Whether or not swift is expected to be available
+swift = True