Fix cancel contract ndf and add call to threadedContractMaintenance
Addressing NDF
--- FAIL: TestRenterContractEndHeight (62.88s)
renter_test.go:1500: unable to cancel contract:failed to acquire contract for update
Adding call to threadedContractMaintenance so that contract is replaced after API call instead of on next loop of threadedContractMaintenance
Edited by Matthew Sevey