Consider only emails that belong to multiple active accounts as ambiguous

Code owner emails that belong to multiple accounts are detected as
ambiguous and their code ownership is ignored. This is intended however
if an email belongs to multiple accounts and only of them is active,
that's fine as there is exactly one active account to which the code
ownership is assigned.

For CodeOwnerResolver this means that it has to load the accounts, and
check if they are active, before deciding if an email is ambiguous.
Doing this changes, actually improves, the debug logs in case there is
an orphaned email.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I50f06e4e055ee04ac17c8873f0e08c0d6aca4b5e

resources/Documentation/validation.md

diff --git a/resources/Documentation/validation.md b/resources/Documentation/validation.md
index 3b0dc95..69929f4 100644
--- a/resources/Documentation/validation.md
+++ b/resources/Documentation/validation.md
@@ -102,7 +102,7 @@
       setting)
     * it is a non-visible secondary email
     * there is no account that has this email assigned
-    * it is ambiguous (the same email is assigned to multiple accounts)
+    * it is ambiguous (the same email is assigned to multiple active accounts)
     * it has an email domain that is disallowed (see
       [allowedEmailDomain](config.html#pluginCodeOwnersAllowedEmailDomain))
       configuration