fix is_fedora for centos 8 stream

When deploying on the centos 8 stream variant
the output of "lsb_release -i -s" is
CentOSStream instead of CentOS

This breaks the is_fedora function in devstack
preventing package installation and removal.

Change-Id: I39ccefbd06f46adf5077f8d8001f37d3b190f040
diff --git a/functions-common b/functions-common
index 1374921..87d8c64 100644
--- a/functions-common
+++ b/functions-common
@@ -452,8 +452,8 @@
     [ "$os_VENDOR" = "Fedora" ] || [ "$os_VENDOR" = "Red Hat" ] || \
         [ "$os_VENDOR" = "RedHatEnterpriseServer" ] || \
         [ "$os_VENDOR" = "RedHatEnterprise" ] || \
-        [ "$os_VENDOR" = "CentOS" ] || [ "$os_VENDOR" = "OracleServer" ] || \
-        [ "$os_VENDOR" = "Virtuozzo" ]
+        [ "$os_VENDOR" = "CentOS" ] || [ "$os_VENDOR" = "CentOSStream" ] || \
+        [ "$os_VENDOR" = "OracleServer" ] || [ "$os_VENDOR" = "Virtuozzo" ]
 }