Prevent /tmp from filling up.

Unexpectedly, the behaviour of amazon ami linnx instance does not
clear /tmp on reboot.

Handle in the program-space by:

 - Downloading all artefacts to a single subdir in /tmp.
 - Removing the /tmp/downloads when invoking clean-previous-state

src/azanium/artefact.py

@@ -10,11 +10,12 @@
 Info = collections.namedtuple('Info', ('download_dir',
                                        'install_dir',
                                        'version'))
-
+DOWNLOAD_DIR = '/tmp/downloads'
 
 def prepare(cmd_ctx, func):
     f_name = func.__name__
-    tmpdir = tempfile.mkdtemp(suffix='-db-migration-downloads')
+    tmpdir = tempfile.mkdtemp(suffix='-db-migration-downloads',
+                              dir=DOWNLOAD_DIR)
     download_dir = os.path.join(tmpdir, f_name)
     install_dir = cmd_ctx.path(f_name)
     version = util.get_deploy_versions()[f_name]
@@ -27,7 +28,7 @@ def prepare(cmd_ctx, func):
 
 def prepared(func):
     """Decorator providing a click command function with download/install info.
-    
+
     Fowards to the original function with addtional ``Info`` object
     containing details such as install and download disk locations.
     """

src/azanium/install.py

@@ -83,7 +83,6 @@ def tace(context, afct, url_template=None):
     local_path = downloaded[0]
     with tarfile.open(local_path) as tf:
         tf.extract('./tace', path=afct.install_dir)
-    shutil.rmtree(os.path.dirname(local_path))
     tace_path = os.path.join(afct.install_dir, 'tace')
     util.touch_dir(afct.install_dir)
     util.make_executable(tace_path, logger)
@@ -107,7 +106,6 @@ def datomic_free(context, afct, url_template=None):
     tmpdir = tempfile.mkdtemp()
     with zipfile.ZipFile(util.download(url, download_path)) as zf:
         zf.extractall(tmpdir)
-    shutil.rmtree(os.path.dirname(download_path))
     shutil.rmtree(install_dir)
     shutil.move(os.path.join(tmpdir, fullname), install_dir)
     util.touch_dir(install_dir)
@@ -141,7 +139,6 @@ def pseudoace(context, afct, **kw):
     tempdir = tempfile.mkdtemp()
     with tarfile.open(dl_path) as tf:
         tf.extractall(path=tempdir)
-    shutil.rmtree(os.path.dirname(dl_path))
     archive_filename = os.path.split(dl_path)[-1]
     fullname = archive_filename.rsplit('.', 2)[0]
     tmp_src_path = os.path.join(tempdir, fullname)

src/azanium/runcommand.py

@@ -240,6 +240,7 @@ def backup_db(context, db_name=None):
 @util.pass_command_context
 def clean_previous_state(context):
     to_remove = set(installers.commands) | {
+        artefact.DOWNLOAD_DIR,
         'acedb_database',
         'acedb_id_catalog',
         'acedb-dump',