Fix escaping in exclusion filter

[zbynek]

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The files that should be ignored are called simply logcat or 0000_logcat. The extra backslash is not working correctly, with the current version of GCloud SDK it's throwing an exception CommandException: Invalid exclude filter (".*\.txt$|.*\.apk$|.*\logcat$|.*\.mp4$|.*\.txt$")

[zbynek]

@piotrmadry will you have time to check and merge it? This makes the download functionality broken by default (workaround is to include Logcat files in download, even if you only care about JUnit results)