[AutoQA] #366: remove previous run logs

[fedora-badges]

#366: remove previous run logs
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 Reporter:  hongqing  |       Owner:                                 
     Type:  task      |      Status:  new                            
 Priority:  major     |   Milestone:  Automate installation test plan
Component:  autotest  |    Keywords:                                 
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 the installation steps are read from anaconda.log, if the previous run
 anaconda.log exists, the installation test steps will be read from the old
 one, so the logs should be cleaned before the next run.

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Ticket URL: <https://fedorahosted.org/autoqa/ticket/366>
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