package-installs: fix error case for Python 2.6

subprocess.CalledProcessError in Python 2.6 does not have the 'out'
parameter for __init__, so pass only two of them and manually set
'output' in that case.

Fixes/improves commit 7f410aaff2.

Change-Id: I279bdf433b1272a9c3af4d66a2a52c78a7ac5de2

elements/package-installs/bin/package-installs-v2

@@ -30,7 +30,9 @@ def process_output(cmdline):
         proc = subprocess.Popen(cmdline, stdout=subprocess.PIPE)
         out = proc.communicate()[0]
         if proc.returncode:
-            raise subprocess.CalledProcessError(proc.returncode, cmdline, out)
+            e = subprocess.CalledProcessError(proc.returncode, cmdline)
+            e.output = out
+            raise e
         return out