This commit changes the state handling of the raft log. The actions
for related to each raft state are strictly confined within that state's
loop. To transition between states, the raft log now much clean up all
its actions before moving on.
This fixes issues where goroutines were kicked off for one state but
were delayed in their scheduling so they would begin after the log
had already changed to another state.
This commit refactors the raft package to more loosely couple the individual parts. The clock is now broken into
an interface that signals individual actions in the log. The transport has been mocked to allow more control over
the log tests. The handler's log has been mocked to separate its testing from the log itself.
Ben Johnson