Massive VA/FV conversion hack; passes local JUnits

VA's only have a system "shadow" key; a Frame key is always made with
the original user-readable key.
System invariant is: there is always a Frame, but only sometimes a VA.
Replace ValueArray va = DKV.get(k).get() with ValueArray.get(k).   This
touches most JUnit tests.
Asking for a VA when a Frame exists but not the VA will auto-convert
from Frame to VA.
Hacking a Frame in Exec2 will delete the shadow VA.
VA keys now have the same format as Vec keys & share some code paths in
the persistence layer.
Merge branch 'cliffc-auto' of github.com:0xdata/h2o into cliffc-auto