Scripting: Fix regression from #1118

The new check-for-number behavior of Lua arguments broke
users who use large strings of just integers.

The Lua number check would convert the string to a number, but
that breaks user data because
Lua numbers have limited precision compared to an arbitrarily
precise number wrapped in a string.

Regression fixed and new test added.

Fixes #1118 again.
Merge pull request #1804 from mattsta/lua-regression-1118

Scripting: Fix regression from #1118
Scripting: Fix for a #1118 regression simplified.

It is more straightforward to just test for a numerical type avoiding
Lua's automatic conversion. The code is technically more correct now,
however Lua should automatically convert to number only if the original
type is a string that "looks like a number", and not from other types,
so practically speaking the fix is identical AFAIK.
Cluster test: rewrite config when resetting nodes.
Cluser test: write multiple keys in unit 03.

The write-failover-read test is better if we write 100 keys so that we
are sure all the nodes are affected by the write.