* Add .mod and .sum files generated by go mod init
* Use a directory outside of $GOPATH for testing.
* Update docker files to use go 1.13.8 instead of 1.12 for most builds.
* Simplify go installation by piping from wget to tar. This avoids
having to do any cleanup.
* Build and test in a directory outside of GOPATH since we're using
modules now.
* Update Jenkinsfile to build using modules by building directly inside
of $WORKSPACE instead of in $GOPATH.
* Use go mod download instead of dep ensure to collect dependencies
* Remove Gopkg related data files.
* Replace calls to "dep ensure" with "go mod download"
* Replace check for being outside of $GOPATH to a check for being INSIDE
of $GOPATH which is wrong when we're using modules
* Map $DIR to /root/influxdb in docker run command
* Clone source into /root/influxdb which is outside of our $GOPATH.
* run go mod tidy
On the master or release branches, `git changelog` will be run to
automatically update the changelog based off of the pull requests that
have been merged and then it will commit and push those changes.