Use ceiling division for fees when funding transactions

Summary:
Add a ceiling option to CFeeRate::GetFee. This ensure that
when calculating minimum fees, or funding transactions, we
can take the ceiling of division, instead of the floor.

This avoids potentially funding transactions below the minRelayFee.

Depends on D1670

Test Plan:

make check && ./test/functional/test_runner.py

Reviewers: #bitcoin_abc, jasonbcox, deadalnix

Reviewed By: #bitcoin_abc, jasonbcox, deadalnix

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1662