Create temporary dirs under compose's workdir

Add compose.mkdtemp which creates and returns a unique temporary
directory under <compose_topdir>/work/{global,<arch>}/tmp[-<variant>]/

Change tempfile.mkdtemp in code to compose.mkdtemp, so temporary
dirs are created under the compose's workdir, this makes it more
easier to maintain the temporary dirs/files especially when compose
fails with amount of temporary files left there.

Signed-off-by: Qixiang Wan <qwan@redhat.com>

tests/helpers.py

@@ -10,7 +10,7 @@ import tempfile
 import shutil
 import errno
 
-from pungi.util import get_arch_variant_data
+from pungi.util import get_arch_variant_data, makedirs
 from pungi import paths, checks
 
 
@@ -106,6 +106,11 @@ class DummyCompose(object):
             result |= set(variant.arches)
         return sorted(result)
 
+    def mkdtemp(self, suffix="", prefix="tmp"):
+        tmpdir = os.path.join('/tmp', "tmp_" + self.compose_id)
+        makedirs(tmpdir)
+        return tempfile.mkdtemp(suffix=suffix, prefix=prefix, dir=tmpdir)
+
 
 def touch(path, content=None):
     """Helper utility that creates an dummy file in given location. Directories