Merge branch 'fix-patch_guide' into 'master'

don't set LATEST_TAG automatically in patch update guide

As discussed in https://gitlab.com/gitlab-org/gitlab-ce/issues/2607, this removes the automatic setting of the LATEST_TAG variable in the update guide, because it could get set to rc versions.

Instead, a command was added to list all tags, with the most recent one being on the end of the list. Also a note was added to prevent users from updating to new minor/major versions because the tag list includes all tags.

[ci skip]

See merge request !1510

doc/update/patch_versions.md

@@ -23,9 +23,11 @@ sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 cd /home/git/gitlab
 sudo -u git -H git fetch --all
 sudo -u git -H git checkout -- Gemfile.lock db/schema.rb
-LATEST_TAG=$(git describe --tags `git rev-list --tags --max-count=1`)
-sudo -u git -H git checkout $LATEST_TAG -b $LATEST_TAG
+sudo -u git -H git checkout LATEST_TAG -b LATEST_TAG
 ```
+Replace `LATEST_TAG` with the latest GitLab tag you want to update to, for example `v8.0.3`.  
+Use `git tag -l 'v*.[0-9]' --sort='v:refname'` to see a list of all tags.  
+Make sure to update patch versions only (check your current version with `cat VERSION`)
 ### 3. Update gitlab-shell to the corresponding version