fetch2: Fix missing output from stderr in fetcher logs

There are actually two problems to fix

1) The exception for bb.process.ExecutionError must be processed first
   because it is a derived from the bb.process.CmdError class and
   we never reach the ExecutionError otherwise.

2) The stderr needs to be printed as well as stdout to determine
   the root cause of a fetch failure.

The example I have is that I got a log that looked like:

--
ERROR: Function failed: Network access disabled through
  BB_NO_NETWORK but access requested with command
   /usr/bin/env wget -t 5 -nv --passive-ftp --no-check-certificate -P
   /localds 'http://downloads.yoctoproject.org/[...CLIPPED...] url None)
--

That really didn't tell me much, but with this patch I get error above
plus the following:

--
STDERR: /net/[...CLIPPED...]kernel-tools.git: Read-only file system
--

(Bitbake rev: af2133a04e1f4b22b181adf9c71f89c439bb88cf)

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -437,11 +437,10 @@ def runfetchcmd(cmd, d, quiet = False, cleanup = []):
         success = True
     except bb.process.NotFoundError as e:
         error_message = "Fetch command %s" % (e.command)
+    except bb.process.ExecutionError as e:
+        error_message = "Fetch command %s failed with exit code %s, output:\nSTDOUT: %s\nSTDERR: %s" % (e.command, e.exitcode, e.stdout, e.stderr)
     except bb.process.CmdError as e:
         error_message = "Fetch command %s could not be run:\n%s" % (e.command, e.msg)
-    except bb.process.ExecutionError as e:
-        error_message = "Fetch command %s failed with exit code %s, output:\n%s" % (e.command, e.exitcode, e.stderr)
-
     if not success:
         for f in cleanup:
             try: