Add integration tests for sighashtype boundary condition

Summary: Added cases for sighashtype with 0x20

Test Plan:
make check
then copied the generated tests to script_tests.json and ran make check again to verify.

Reviewers: deadalnix, schancel, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1381