Fix inability to use branches and tags interchangably.

Changelog: None

Signed-off-by: Kristian Amlie <kristian.amlie@mender.io>

.travis.yml

@@ -9,6 +9,16 @@ dist: trusty
 before_script:
     - git clone git://github.com/mendersoftware/mendertesting
 
+    # Rename the branch we're on, so that it's not in the way for the
+    # subsequent fetch. It's ok if this fails, it just means we're not on any
+    # branch.
+    - git branch -m temp-branch || true
+    # Git trick: Fetch directly into our local branches instead of remote
+    # branches.
+    - git fetch origin 'refs/heads/*:refs/heads/*'
+    # Get last remaining tags, if any.
+    - git fetch --tags origin
+
 script:
     # Check commit compliance.
     - mendertesting/check_commits.sh