Merge pull request #674 from TheBlueMatt/2020-08-keyif-rand-names

Simplify + clarify random-bytes-fetching from KeysInterface

diff --cc fuzz/src/chanmon_consistency.rs
Simple merge

diff --cc lightning/src/ln/channel.rs
Simple merge

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_tests.rs
Simple merge

diff --cc lightning/src/util/test_utils.rs
Simple merge