Fixes to improve python2.7 compatibility

[alexkas1977]

Add object keyword in two classes definitions - it allows super() to work correctly
Change the way that random time interval works
Fixed indentation error

[codecov-io]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is 80%.

@@           Coverage Diff           @@
##           master      #14   +/-   ##
=======================================
  Coverage   80.57%   80.57%           
=======================================
  Files          25       25           
  Lines         767      767           
=======================================
  Hits          618      618           
  Misses        149      149

Impacted Files	Coverage Δ
chaosmonkey/attacks/executor.py	36.36% <0%> (ø)	⬆️
chaosmonkey/attacks/attack.py	83.33% <100%> (ø)	⬆️
chaosmonkey/engine/cme_manager.py	93.15% <100%> (ø)	⬆️
chaosmonkey/planners/planner.py	72.22% <100%> (ø)	⬆️

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