don't send feeless transactions

(cherry picked from commit 9a2f7a86fca6e243db7745cb1b15b35ce1b97b2e)
Revert "remove unit tests for new fee mode"

This reverts commit 78ed897c4adf021c30cdf10eebf4663f12f78fd1.
remove unit tests for old fee mode
adapt rpc tests to mandatory fees
Merge pull request #553 from leofidus/1.7-nozerofee

Don't send feeless transactions