Fix is_fedora RHEL 8 detection

While RHEL 7 is detected as RedHatEnterpriseServer, RHEL 8 is
RedHatEnterprise.

  $ lsb_release -i -s
  RedHatEnterprise

Change-Id: I3d750d808c6ebea9c230f0508cdbc016415b9922
diff --git a/functions-common b/functions-common
index d99ad92..acb3a6c 100644
--- a/functions-common
+++ b/functions-common
@@ -451,6 +451,7 @@
 
     [ "$os_VENDOR" = "Fedora" ] || [ "$os_VENDOR" = "Red Hat" ] || \
         [ "$os_VENDOR" = "RedHatEnterpriseServer" ] || \
+        [ "$os_VENDOR" = "RedHatEnterprise" ] || \
         [ "$os_VENDOR" = "CentOS" ] || [ "$os_VENDOR" = "OracleServer" ] || \
         [ "$os_VENDOR" = "Virtuozzo" ]
 }