Ledger upgrade transaction should specify a package name

Story
As an administrator of a node on an Indy Network, I want the upgrade transaction to specify my network specific package rather than generic Indy Node so that my network specific package can perform configuration and customization functions such as installing network specific plugins to the Plenum Ledger.

Acceptance Criteria

• The upgrade transaction should include a value containing the package that should be upgraded.
  Add a new (optional) parameter to POOL_UPGRADE txn with a package name. As of now this is IndyNode, and it should remain the default. https://github.com/hyperledger/indy-node/blob/master/docs/transactions.md#pool_upgrade

Notes

• The work for the Node upgrade script should use that value to call the platform specific package manager to install or update the package is tracked in INDY-1500.
• The Sovrin network wants their network upgrades to call the Sovrin package instead of Indy Node. The Sovrin package depends on Indy Node.
• There will be a new release of the Sovrin network package with each release of Indy Node.