Fix RHEL7 vendor detection

When detecting os_VENDOR, the lsb_release output may be different
from what is expected today. This patch fixes the detection.

Change-Id: I850ad1acbc2397c73e7cc85c1765cba6ba2f98d4
diff --git a/functions-common b/functions-common
index 98768cd..366415b 100644
--- a/functions-common
+++ b/functions-common
@@ -440,6 +440,7 @@
     fi
 
     [ "$os_VENDOR" = "Fedora" ] || [ "$os_VENDOR" = "Red Hat" ] || \
+        [ "$os_VENDOR" = "RedHatEnterpriseServer" ] || \
         [ "$os_VENDOR" = "CentOS" ] || [ "$os_VENDOR" = "OracleLinux" ] || \
         [ "$os_VENDOR" = "Virtuozzo" ] || [ "$os_VENDOR" = "kvmibm" ]
 }