be more user-friendly when looking for matching .config

On fspath installs, look for .config files harder.
Given a file named:
  pkg.namespace_0.version_arch.snap
We'll search for config files named:
  pkg.namespace_0.version_arch.config
  pkg.namespace.config
  pkg.config

cloudinit/config/cc_snappy.py

@@ -67,15 +67,26 @@ BUILTIN_CFG = {
 }
 
 
+def parse_filename(fname):
+    fname = os.path.basename(fname)
+    fname_noext = fname.rpartition(".")[0]
+    name = fname_noext.partition("_")[0]
+    shortname = name.partition(".")[0]
+    return(name, shortname, fname_noext)
+    
+
 def get_fs_package_ops(fspath):
     if not fspath:
         return []
     ops = []
-    for snapfile in glob.glob(os.path.sep.join([fspath, '*.snap'])):
+    for snapfile in sorted(glob.glob(os.path.sep.join([fspath, '*.snap']))):
-        cfg = snapfile.rpartition(".")[0] + ".config"
+        (name, shortname, fname_noext) = parse_filename(snapfile)
-        name = os.path.basename(snapfile).rpartition(".")[0]
+        cfg = None
-        if not os.path.isfile(cfg):
+        for cand in set((fname_noext, name, shortname,)):
-            cfg = None
+            fpcand = os.path.sep.join([fspath, cand]) + ".config"
+            if os.path.isfile(fpcand):
+                cfg = fpcand
+                break
         ops.append(makeop('install', name, config=None,
                    path=snapfile, cfgfile=cfg))
     return ops

tests/unittests/test_handler/test_handler_snappy.py

@@ -112,6 +112,40 @@ class TestInstallPackages(t_help.TestCase):
              makeop_tmpd(self.tmp, 'install', 'snapf2', path="snapf2.snap"),
              makeop('install', 'pkg1')])
 
+    def test_package_ops_common_filename(self):
+        # fish package name from filename
+        # package names likely look like: pkgname.namespace_version_arch.snap
+        fname = "xkcd-webserver.canonical_0.3.4_all.snap"
+        name = "xkcd-webserver.canonical"
+        shortname = "xkcd-webserver"
+
+        # find filenames
+        self.populate_tmp(
+            {"pkg-ws.smoser_0.3.4_all.snap": "pkg-ws-snapdata",
+             "pkg-ws.config": "pkg-ws-config",
+             "pkg1.smoser_1.2.3_all.snap": "pkg1.snapdata",
+             "pkg1.smoser.config": "pkg1.smoser.config-data",
+             "pkg1.config": "pkg1.config-data",
+             "pkg2.smoser_0.0_amd64.snap": "pkg2-snapdata",
+             "pkg2.smoser_0.0_amd64.config": "pkg2.config",
+            })
+
+        ret = get_package_ops(
+            packages=[], configs={}, installed=[], fspath=self.tmp)
+        raise Exception("ret: %s" % ret)
+        self.assertEqual(
+            ret,
+            [makeop_tmpd(self.tmp, 'install', 'pkg-ws.smoser',
+                         path="pkg-ws.smoser_0.3.4_all.snap",
+                         cfgfile="pkg-ws.config"),
+             makeop_tmpd(self.tmp, 'install', 'pkg1.smoser',
+                         path="pkg1.smoser_1.2.3_all.snap",
+                         cfgfile="pkg1.smoser.config"),
+             makeop_tmpd(self.tmp, 'install', 'pkg2.smoser',
+                         path="pkg2.smoser_0.0_amd64.snap",
+                         cfgfile="pkg2.smoser_0.0_amd64.config"),
+             ])
+
     def test_package_ops_config_overrides_file(self):
         # config data overrides local file .config
         self.populate_tmp(