Make blessed an optional dependency

blessed is not in openstack g-r and blocks us from aligning there. This makes
the dependency optional.  If it is not installed, the cli browse command emits
a warning telling the user to install it.  The browse section of the CLI is the
only place its used and doesn't affect any other functionality.

Change-Id: If446c2135936c8ea4083eb9fc712a98031b28ac4

akanda/rug/cli/browse.py

@@ -26,7 +26,13 @@ import threading
 from contextlib import closing
 from datetime import datetime
 
-from blessed import Terminal
+try:
+    from blessed import Terminal
+except ImportError:
+    # blessed is not part of openstack global-requirements.
+    raise Exception("The 'blessed' python module is required to browse"
+                    " Akanda routers. Please install and try again.")
+
 from oslo.config import cfg
 
 from akanda.rug import commands

akanda/rug/test/unit/api/test_rug_api.py

@@ -8,6 +8,12 @@ from cliff import commandmanager
 from akanda.rug.api import rug
 from akanda.rug.openstack.common import log as logging
 
+try:
+    import blessed  # noqa
+    HAS_BLESSED = True
+except ImportError:
+    HAS_BLESSED = False
+
 
 class TestRugAPI(unittest.TestCase):
 
@@ -19,6 +25,7 @@ class TestRugAPI(unittest.TestCase):
         self.api = rug.RugAPI(ctl)
         self.ctl = ctl.return_value
 
+    @unittest.skipUnless(HAS_BLESSED, "blessed not available")
     def test_browse(self):
         resp = self.api(webob.Request({
             'REQUEST_METHOD': 'PUT',

requirements.txt

@@ -8,4 +8,3 @@ kombu>=2.4.8
 WebOb>=1.2.3,<1.3
 python-novaclient>=2.15.0
 cliff>=1.4.3
-blessed>=1.9.1