amari.xlog: Test and polish str(LogSpec)

If the parsed period was '60s' we were printing it back as '60.0s' on str.
Fix it by using %g insted of %s.

amari/xlog.py

@@ -96,7 +96,7 @@ class LogSpec:
         spec.period = period
 
     def __str__(spec):
-        return "%s[%s]/%ss" % (spec.query, ','.join(spec.optv), spec.period)
+        return "%s[%s]/%gs" % (spec.query, ','.join(spec.optv), spec.period)
 
     # LogSpec.parse parses text into LogSpec.
     @staticmethod

amari/xlog_test.py

@@ -306,6 +306,7 @@ def test_LogSpec():
     assert spec.query == "stats"
     assert spec.optv == ["samples", "rf"]
     assert spec.period == 60.0
+    assert str(spec) == logspec
 
 
 def test_ReverseLineReader():