Yara/Logging/Misc Fix Updates

[0xd34db33f]

Nice project. Fixed/Updated a couple of things for you:

• Fixed the grep list issue where it would error if you didn't include it (the help info suggests its optional)
• Adding a Yara scanning flag to search the downloaded files for things of interest. Only one Yara rule (PDF detection) in there at the moment
• Changed the logging functionality with some code from one of my other projects. Use the Python logging module to drop everything into a single log file with data timestamps included.

[jordanpotti]

Thanks for the pull request, nice work! Can you take a look at the Travis CI Build results? I am getting the same results when I try to run the tool locally. The error message states:
OSError: /home/travis/virtualenv/python3.6.3/lib/libyara.so: cannot open shared object file: No such file or directory

[jordanpotti]

https://travis-ci.org/jordanpotti/AWSBucketDump/builds/455816994?utm_source=github_status&utm_medium=notification

[0xd34db33f]

Ah I see the problem, I had Yara installed previously so it dropped the library on my system. Looks like it requires libyara to be installed on Ubuntu systems (simple apt-get install libyara should do the trick). Not sure how you'd like that documented though, LMK.

[0xd34db33f]

Thought just occurred to me. The Yara functionality needs to be truly optional especially given the opt-in command line switch. So I went ahead and added a graceful try-except that disables Yara if the import isn't graceful. We should still include a note somewhere in the instructions (I'll leave this up to your better discretion) but basically say "You need to fully install the Yara libraries to get this support"

[AkechiShiro]

Is there anything still blocking this PR merge ?