typo in the policy.json "rule_admin_api"

policy.json has "rule_admin_api" string instead of
the "rule:admin_api" which causes ValueError.

The typo recently introduced by
 4bb34182fe28c89686c8a23ddcfc8e9128d289b5.

Change-Id: I232adfca033e9365927cf2abd62d391337fae429
Closes-Bug: #1385225
Merge "typo in the policy.json "rule_admin_api""