In many cases when a storagenode fails the preflight check, it is due to
test_table existing, which is used to determine read/write capabilities
after the initial schema verification. If preflight ends early due to a
failure or stopped storagenode, it may not get the chance to drop this
table.
This change excludes test_table from the schema comparison to ensure
that it never prevents a storagenode from starting up.
It also adds Preflight DB test for storagenode.
Change-Id: Ib8e71df2e42fda3b2a364fbf7a801891c5831d39
