Re-write sqlite BigInteger mapping test

This test makes sure that our hook that compiles BigInteger() into
INTEGER for sqlite instead of BIGINT is working as we expect.
Unfortunately, we've seen some problems running the sqlite command to
check the schema.

This patch rewrites the test to only use sqlalchemy APIs and avoid
calling out to the sqlite command for verification.

Change-Id: Id3964d0dd5b0ddf08ab745d6878840ff06b2f0dd
Closes-bug: #1271331
Merge "Re-write sqlite BigInteger mapping test"