fix: cookies removed on failed connection

[soodoh]

Fixes issue:
#2

Potentially fixes #1, but could not reproduce.

Made some formatting, readability changes as well, but can move to a separate PR if preferred.
So far this is working for me when building the image locally and dropping it in as a replacement in my compose file.

Superseded previous PR: #3

[soodoh]

Mostly some opinionated formatting changes here to improve readability. Can revert anything if preferred.

[soodoh]

Renamed variables to have more meaning. For example, there are multiple temporary, cached files, so CACHEFILE would be confusing. Also using SCREAMING_SNAKE_CASE since I find this easier to read instead of concatenating words together.

[soodoh]

This is the crux of the fix. When using the -c flag with curl, it writes all the cookies to the file passed here (even on failed requests, it will write empty cookies). Here's a relevant snippet from man curl:

       -c, --cookie-jar <filename>
              (HTTP) Specify to which file you want curl to write all cookies after a completed operation. curl  writes
              all  cookies  from  its  in-memory  cookie storage to the given file at the end of operations. Even if no
              cookies are known, a file is created so that it removes any formerly existing cookies from the file.  The
              file  uses  the  Netscape cookie file format. If you set the filename to a single minus, "-", the cookies
              are written to stdout.

[soodoh]

Other relevant part of this fix. Everything else is formatting or variable name changes.