Merge pull request #140 from travis-ci/rkh-track-user-agent

track and enforce user-agent
Revert "track and enforce user-agent"
Merge pull request #141 from travis-ci/revert-140-rkh-track-user-agent

Revert "track and enforce user-agent"
Revert "Revert "track and enforce user-agent""

This reverts commit 2227d0042f166659466b38a1f2db975b735f3638.
reduce metrics generated by UA tracker