Resolve "Gitlab daemon crashing. Omnibus installation (Ubuntu 14.04)"

This MR fixes a collection of small problems thrown up while investigating the named issue:

• Some error messages are not reported correctly due to using println instead of log.Println
• Exercise the chrooted mode in the acceptance tests
• Document the CGO_ENABLED=0 requirement of the chrooted mode
• Clean up acceptance test running a little
• Add Go 1.8 to the list of CI builds
• Run the acceptance tests on all CI builds

Closes #4 (closed)

.gitlab-ci.yml

@@ -12,11 +12,13 @@ test:1.5:
   image: golang:1.5
   script:
   - make verify-lite
+  - make acceptance
 test:1.6:
   image: golang:1.6
   script:
   - make verify
+  - make acceptance
 test:1.7:
   image: golang:1.7