classes/sanity: trim trailing newline when reading /etc/redhat-release

Any trailing whitespace needs to be stripped before comparing it to the
SANITY_TESTED_DISTROS list.

(From OE-Core rev: bea0311a6478febe8ab4884fb1c479f610856534)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sanity.bbclass

@@ -120,7 +120,7 @@ def check_supported_distro(e):
     if os.path.exists("/etc/redhat-release"):
         f = open("/etc/redhat-release", "r")
         try:
-            distro = f.readline()
+            distro = f.readline().strip()
         finally:
             f.close()
     elif os.path.exists("/etc/SuSE-release"):