(QA-841) Windows complains about colons in sir names

Creating a directory with colons (':') in the name will fail on Windows
and prevent beaker from executing tests. This change moves from calling
%T to using %H_%M_%S for time-based directory names.
Merge pull request #153 from colinPL/invalid_dir_name

(QA-841) Windows complains about colons in dir names