skip git-annex tests if distro or git-annex is too old
avoid TB for encoding in python3

527e60ba added method `run_command_print' to provide
buffered output during long-running commands.

This causes TB in python3 due to IO encoding issues, so for now...

* use getoutput instead of run_command_print
* add TODO in run_command_print to make it compatible asap
avoid TB in gitannex builder test on python3

Avoids...

Traceback (most recent call last):
  File "/home/sandbox/test/functional/build_gitannex_tests.py", line 87, in test_simple_build
    self.assertEquals(1, len(builder.sources))
nose.proxy.TypeError: TypeError: object of type 'map' has no len()
add test harness based on docker/lxc
Merge pull request #112 from jumanjiman/test_harness

add containerized test harness