append to apt_sources filenames rather than truncating.

Previously, 
apt_sources:
  - source: source1
  - source: source2

resulted in source1 being written to
/etc/apt/sources.list.d/cloud_config_sources.list , and then
that being overwritten by source2.

This definitely is not expected.

Instead, in all cases now, (including 'filename:' cases), just append.

LP: #627597

2 files changed, 5 insertions, 4 deletions

diff --git a/cloudinit/CloudConfig/cc_apt_update_upgrade.py b/cloudinit/CloudConfig/cc_apt_update_upgrade.py
index e1226c85..396c5e09 100644
--- a/cloudinit/CloudConfig/cc_apt_update_upgrade.py
+++ b/cloudinit/CloudConfig/cc_apt_update_upgrade.py
@@ -142,7 +142,7 @@ def add_sources(srclist):
             except:
                 elst.append([source, "failed add key"])
 
-        try: util.write_file(ent['filename'], source + "\n")
+        try: util.write_file(ent['filename'], source + "\n", omode="ab")
         except:
             elst.append([source, "failed write to file %s" % ent['filename']])
 
diff --git a/cloudinit/util.py b/cloudinit/util.py
index be84bfdc..c1b4fd2d 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -76,15 +76,16 @@ def mergedict(src,cand):
                 src[k] = mergedict(src[k],v)
     return src
 
-def write_file(file,content,mode=0644):
+def write_file(file,content,mode=0644,omode="wb"):
         try:
             os.makedirs(os.path.dirname(file))
         except OSError as e:
             if e.errno != errno.EEXIST:
                 raise e
 
-        f=open(file,"wb")
-        os.chmod(file,mode)
+        f=open(file,omode)
+        if mode != None:
+            os.chmod(file,mode)
         f.write(content)
         f.close()