use tailhead instead of tailer so as to handle rotating logs

[fgregg]

The current version of tailer does not follow the name of a file, it follows a file descriptor. This means that if you rotate the log files, sentrylogs will not see any of the new information in the new file.

This PR six8/pytailer#12 adds code into the tailer's follow method to change the behavior to follow a filename.

This PR swaps out the tailing dependency from tailer to tailhead in order to take advantage of tailhead ability to follow a filename.

[mdgart]

@fgregg linters are failing, can you take a look?

[fgregg]

pip has removed installing from dependency links by default. I'll wait a couple of days to see if the maintainers of tailer want to bring in that PR. If they don't I'll get a version with log rotation on pypi and revisit this PR.

[fgregg]

I think that Pipfile and Pipfile.lock will need be updated, but I'm not really familiar with those files. attn @bittner

[bittner]

This can be simply

if line:

... which is pythonic. Also, an empty line wouldn't need to be parsed, right?

[mdgart]

I agree

[fgregg]

i think an empty line could be important to parse. Empty lines are often used as separators. Not used that way for nginx, but this part of the code is not nginx specific.

[bittner]

Re Pipfile, the line with tailer needs to be updated accordingly (i.e. with tailhead and its minimum version or version range, if that is known). Same goes for requirements.txt, as long as we have both.

1. requirements.txt
2. Pipfile

Afterwards, run pipenv update to regenerate Pipfile.lock, and put everything under version control.

[fgregg]

Let me decide what you want to do with falsy lines. Otherwise I think this is good to go @mdgart

[mdgart]

ok, I'm merging it