Verified behaviour for all group commands

I have looked at the new output and api calls for the "group" commands
in the testsuite and it looks good to me.
Fixed a bug in history.py concerning how history is printed when owners
or hosts are added/removed from hostgroups.
Made a minor change to the datetime regex in diff.py to handle the extra
space that comes before a single digit date.

ci/diff.py

@@ -10,7 +10,7 @@
     r"\d{4}-\d{2}-\d{2}[ T]\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:[+-]\d{2}:\d{2})?|\d{4}-\d{2}-\d{2}"
 )
 datetime_str_pattern = re.compile(
-    r"\b[A-Za-z]{3}\s[A-Za-z]{3}\s([0-2]?[0-9]|3[0-1])\s([0-1]?[0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])\s[0-9]{4}\b"
+    r"\b[A-Za-z]{3}\s[A-Za-z]{3}\s+([0-2]?[0-9]|3[0-1])\s([0-1]?[0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])\s[0-9]{4}\b"
 )
 # datetime_str_pattern = re.compile(
 #     r"\b(Sun|Mon|Tue|Wed|Thu|Fri|Sat)\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)\s([0-2]?[0-9]|3[0-1])\s([0-1]?[0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])\s[0-9]{4}\b"