Unify sample collection

Unify sample collection in preparation for sampling the system clock.

Signed-off-by: Pekka Enberg <penberg@iki.fi>
Formatting fixes

Courtesy of gofmt.

Signed-off-by: Pekka Enberg <penberg@iki.fi>
Sample system clock

Use Golang's time.Now() which should use the monotonic clock under the
hood.

Signed-off-by: Pekka Enberg <penberg@iki.fi>