spanner: more integration tests
spanner: more integration tests

These correspond to the desired Spanner Client Test Cases
for read failures and various query cases.

Change-Id: Idc398b3319e71de616a008ec7263240e0168cd39
Reviewed-on: https://code-review.googlesource.com/13930
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Michael Darakananda <176c4818757ce942f02114959cee75d35f2575d9@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go