Automatic versioning for aptly

New version format:

* for releases, `x.y.z` (follows tag without leading `v`)
* for nightly builds, `x.y.z+N+hash` (previous version, not the upcoming one)

This means that each nightly build `aptly` would report
correct version now.

Version is now complied into the aptly binary, system tests
automatically check for current version, no need to update them
anymore.

system/t12_api/unix_socket.py

@@ -1,9 +1,11 @@
 import requests_unixsocket
 import time
+import os
 import urllib
 
 from lib import BaseTest
 
+
 class UnixSocketAPITest(BaseTest):
     aptly_server = None
     socket_path = "/tmp/_aptly_test.sock"
@@ -33,4 +35,4 @@ class UnixSocketAPITest(BaseTest):
         r = session.get('http+unix://%s/api/version' % urllib.quote(UnixSocketAPITest.socket_path, safe=''))
         # Just needs to come back, we actually don't care much about the code.
         # Only needs to verify that the socket is actually responding.
-        self.check_equal(r.json(), {'Version': '0.9.8~dev'})
+        self.check_equal(r.json(), {'Version': os.environ['APTLY_VERSION']})