Added fix to remove app/apk files from zipPath before appium starts to unzip them. If this is *.app located in Payload folder then folder is being removed too. Fix is done because fruitstrap sometimes failes to install app file on the device when /var/folders/... are not cleared correctly.
Merge pull request #1030 from tborys/remove_unziped_files

Remove *.app/*.apk/ file and Payload folder before appium starts to unzip file.