log: Clean up election in the operation loop

[pav-kv]

Comments, variable renames, and factoring out some code.
Review commit by commit.

This is in preparation for fixing #1150.

[pav-kv]

Note: This is a cosmetic PR. It's convenient to review commit-by-commit.

[pav-kv]

All comments are addressed.

[pav-kv]

Interesting: https://travis-ci.org/github/google/trillian/jobs/755698264
WARNING: DATA RACE.
I'm taking a look at it.

[pav-kv]

Got it: NewRunner takes ElectionConfig by pointer, and tries to modify it in Run method. The config is also used in other places. It probably shouldn't be used by pointer.

[Martin2112]

Are the modifications in NewRunner necessary for it to work? It might not be entirely straightforward to fix.

[pav-kv]

The modifications are not necessary (there is a TODO to move them out), but I'm reluctant to touch it for now.
I made a simpler fix: copy the config for each log.

[Martin2112]

OK that sounds like it should work.

[pav-kv]

There is an unrelated test failure TestLogSuite/DequeueLeavesTwoBatches for the in-memory CloudSpanner instance. It's flaky because the in-memory CloudSpanner doesn't actually implement transactions.

[Martin2112]

OK.

[pav-kv]

Added a commit with a minor comment to trigger builds again.