Remove hardcoded gitlab.com certificate

Closes #2815

See merge request gitlab-org/gitlab-runner!710

Set git SSL information only for gitlab host

Closes #2148

See merge request gitlab-org/gitlab-runner!687

Construct git remote URL based on configuration

Closes #1141

See merge request gitlab-org/gitlab-runner!698

Previously, GitLab CE/EE exposed the clone/fetch url, however, in more
complex situations where e.g. a firewall is in play this won't work.

If the user configures a `CloneURL` this URL is used to construct a
clone or fetch path. The URL _must_ start with `http` or `https`.

Hide tokens from URLs printed in job's trace

Closes #2741

See merge request gitlab-org/gitlab-runner!708

Collect metrics on build stages

Closes #2505

See merge request gitlab-org/gitlab-runner!689

update git-lfs to 2.3.1

See merge request gitlab-org/gitlab-runner!703

fix runners.kubernetes link

See merge request gitlab-org/gitlab-runner!693

Directly return result of b.writeSubmoduleUpdateCmds()

See merge request gitlab-org/gitlab-runner!697

Fix small typo in Docker Machine part of executors/README.md

See merge request gitlab-org/gitlab-runner!701

Adds EmptyDir support for k8s volumes

Closes #2575

See merge request gitlab-org/gitlab-runner!660

Expose if running in a disposable environment

See merge request gitlab-org/gitlab-runner!690

It can be detected during the build with `CI_DISPOSABLE_ENVIRONMENT` and
`CI_SHARED_ENVIRONMENT` environment variables.
It can also be detected programmatically with `common.Build.SharedEnv`

Update BurntSushi/toml for MIT-license

Closes #2785

See merge request gitlab-org/gitlab-runner!695

Fix gitlab-runner pattern in .gitignore

See merge request gitlab-org/gitlab-runner!696

Remove deprecation message from service management commands

See merge request gitlab-org/gitlab-runner!699