Make compute-trust.json compatible with TrustFilter

Current properties inside compute-trust.json does not match
with how TrustFilter in nova works. JSON provides True/False
boolean values but TrustFilter expects trusted/untrusted/unknown
string values. This patch repairs compute-trust.json to be
compatible with TrustFilter.

Change-Id: I26965a549daf9340621b0f18a1b845b39bac4bd8
Closes-Bug: #1369581
(cherry picked from commit 39e90f29d93f991d95092de5f93a239be1b3ca3b)
Merge "Make compute-trust.json compatible with TrustFilter" into proposed/juno