MINOR: stream: Use a pcli transaction to replace pcli_* members

MINOR: stream: Use a pcli transaction to replace pcli_* members

A new type of transaction was introduced for master-cli streams. So
SF_TXN_PCLI flag and functions to allocate and destroy PCLI transactions
were added.

In the stream structure, all pcli_* members were moved in the pcli
transaction and the txn union was updated accordingly.

When it was ambiguous, a test on the transaction type was performed. For
instance to destroy the transaciton.