[FAB-9505] Export Gate and Role values used in policies
[FAB-9505] Export Gate and Role values used in policies

This changeset groups and exports the gate and role values that can be
used when constructing strings corresponding to policies.

It also removes references to the "orderer" role value as this is not
supported - see `MSPRoleType` values in `msp_principal.proto`.

Change-Id: Ic8df3bc38721abe80df25038068908650fae9084
Signed-off-by: Kostas Christidis <e1a8399e36effe75a124102eb2a2bdfc82e0aab4@christidis.io>

jimthematrix/fabric,binhn/fabric,jimthematrix/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric,stemlending/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,stemlending/fabric,xixuejia/fabric,muralisrini/fabric,xixuejia/fabric,binhn/fabric,binhn/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,manish-sethi/fabric-sidedb,muralisrini/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric,muralisrini/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,xixuejia/fabric