Pass flags down to GetSigOpCount
Summary: This will ensure we can use flags to tweak the way sigops are counted in the future. This is necessary for the activation of OP_CHECKDATASIG.
Test Plan: Added test cases to ensure behavior changes as expected when the P2SH flags is flipped.
Reviewers: #bitcoin_abc, jasonbcox, schancel
Reviewed By: #bitcoin_abc, jasonbcox, schancel
Subscribers: schancel, teamcity
Differential Revision: https://reviews.bitcoinabc.org/D1601