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/t10_task/RunTask1Test_gold

@@ -21,6 +21,6 @@ End command output: ------------------------------
 4) [Running]: version
 
 Begin command output: ----------------------------
-aptly version: 0.9.8~dev
+aptly version: ${APTLY_VERSION}
 
 End command output: ------------------------------

system/t10_task/run.py

@@ -5,6 +5,8 @@ class RunTask1Test(BaseTest):
     """
     task run: simple commands, 1-word command
     """
+    gold_processor = BaseTest.expand_environ
+
     runCmd = "aptly task run repo list, repo create local, repo drop local, version"