Fixes for crontab and proposals to hashed crontab

Fix for JENKINS-11353
thanks.

[JENKINS-12518] table rows with id= for keyboard shortcuts plugin

[FIXED JENKINS-12357] Crontab#ceil may stuck in an infinite loop or may return an incorrect value if day of week is 7 (=0, Sunday)

To use @test(timeout), inheritance from TestCase should be removed

They look different, but had been same. See 921359c1

Fix multi submit with shortcut key

This reverts commit 47c520b1.

I see it clearly now. I was bit concerned about double-counting,
because one expects that totalSnapshot (total # of executors)
includes idle executors. But this is not the case, and in any way
this code should be read as (x==0 && y==0 && z==0) not (x+y+z==0)
conceptually. So reverting my revert.

This reverts commit 5a95baff.
Oops, I don't know about this. More comments in
https://github.com/jenkinsci/jenkins/pull/362