PR #3154 introduced an `l5d-require-id` header to Tap requests. That
header string was constructed based on the TapByResourceRequest, which
includes 3 notable fields (type, name, namespace). For namespace-level
requests (via commands like `linkerd tap ns linkerd`), type ==
`namespace`, name == `linkerd`, and namespace == "". This special casing
for namespace-level requests yielded invalid `l5d-require-id` headers,
for example: `pd-sa..serviceaccount.identity.linkerd.cluster.local`.
Fix `l5d-require-id` string generation to account for namespace-level
requests. The bulk of this change is tap unit test updates to validate
the fix.
Signed-off-by: Andrew Seigner <siggy@buoyant.io>
Andrew Seigner