Introduce rotate_compress option for log and errors directives in Caddyfile

[fern4lvarez]

1. What does this change do, exactly?

This PR addresses #1728 and provides a new rotate_compress option for log and errors directive to the Caddyfile, which will enable gzip compression for rotated log files.

It also updates the Lumberjack package dependencies in the vendor directory, and adds go-syslog, which was not present in vendor and was breaking tests when this was not present.

2. Please link to the relevant issues.

#1728

3. Which documentation changes (if any) need to be made because of this PR?

caddyserver/website#18

4. Checklist

• I have written tests and verified that they fail without my change
• I have squashed any insignificant commits
• This change has comments for package types, values, functions, and non-obvious lines of code
• I am willing to help maintain this change if there are issues with it later

[CLAassistant]

All committers have signed the CLA.

[mholt]

Thanks for your contribution! This is looking pretty good, but I think we can improve the Caddyfile syntax a little.

Also, this change shouldn't introduce any new dependencies, and the CI tests were passing -- I haven't seen any failures in my inbox. We don't need dependencies for the test files to be vendored. What command did you run that failed?

[mholt]

Let's get rid of "true" here, since the presence of "rotate_compress" will make that obvious. (And lack of it is obviously "false".) In other words, the line would be "rotate_compress" by itself, no arguments.

[mholt]

This comment isn't super helpful, it can be removed. ;)

[fern4lvarez]

@mholt re: broken dependency

I just reverted the commit that adds the gopkg.in/mcuadros/go-syslog.v2 package to vendor/ and ran the tests:

$ git revert 6722284                                            
[1728-log-rotate-compress 9e990b6] Revert "vendor: add go-syslog dep"
...
$ go test -v ./caddyhttp/httpserver               
# github.com/mholt/caddy/caddyhttp/httpserver
caddyhttp/httpserver/logger_test.go:15:2: cannot find package "gopkg.in/mcuadros/go-syslog.v2" in any of:
	/home/fernando/src/github.com/mholt/caddy/vendor/gopkg.in/mcuadros/go-syslog.v2 (vendor tree)
	/usr/local/go/src/gopkg.in/mcuadros/go-syslog.v2 (from $GOROOT)
	/home/fernando/src/gopkg.in/mcuadros/go-syslog.v2 (from $GOPATH)
FAIL	github.com/mholt/caddy/caddyhttp/httpserver [setup failed]

Of course, I can go get gopkg.in/mcuadros/go-syslog.v2 and the tests would pass. But this dependency is not tracked into vendor/. If you think we should not add it to vendor/ and rely on the user having imported it in their $GOPATH, I'm happy to revert that commit :)

[fern4lvarez]

@mholt based on your comments:

• I agree that either we need to vendor gopkg.in/mcuadros/go-syslog.v2 or not, this ain't part of this PR, so I removed it.
• No need to set false or true along with rotate_compress. If the option is declared into the Caddyfile, we want to compress logs.
• Get rid of defaultRotateCompress. We don't compress by default, hence it is false, so no need to create a wrapping var for this.

I'll also update caddyserver/website#18 accordingly.

[mholt]

When you go get a repository, it doesn't fetch test dependencies. If you go get a repository to develop it, you should use go get -t to download test dependencies too. But we do not need to vendor dependencies used solely for tests.

The changes look superb!! Thanks for your great work and thorough detailing.