Introduce pragma no cover to asbtract classes

Since the unimplemented methods for abstract classes are not meant to be
actually used, they shouldn't be included in the code coverage
calculation. Thus, to address this I introduced the pragma "no cover" to
these classes.

Change-Id: Id239a2eb42d8288764b8f374d5d13ebd37af5a7d
Move token_api.unique_id to token_provider_api

Move the unique_id call from token_api to token_provider_api and
mark token_api.unique_id as deprecated, slated for removal in
the K cycle.

As part of the move to non-persistent tokens, the token_api calls
are being moved (as appropriate) to the token_provider_api in
preperation of token_api being deprecated.

Change-Id: I7186b8af3ecc572ca364d58e2ba1a0303e48aca1
bp: non-persistent-tokens
Move keystone.token.default_expire_time to token.provider

Move the default_expire_time function from
keystone.token.core to keystone.token.provider. The function
keystone.token.core.default_expire_time is slated for removal
in the K cycle.

As part of the move to non-persistent tokens, the token_api calls
are being moved (as appropriate) to the token_provider_api in
preperation of token_api being deprecated.

Change-Id: Ic61e0dc13c7aabadbf75ae7aec30b30ce78d937b
bp: non-persistent-tokens
Merge "Move token_api.unique_id to token_provider_api"
Merge "Move keystone.token.default_expire_time to token.provider"
Merge "Introduce pragma no cover to asbtract classes"