Currently `restoreDatabase`, `updateBackup` and `deleteBackup` are final methods. For some internal tests, we need to override these methods so ideally they shouldn't be final.

SpannerRetryHelperTest.testExceptionWithRetryInfo could sometimes fail on some
environments. I have not been able to reproduce it locally, but one possible
reason for the failure could be truncation when converting from nanoseconds to
milliseconds. Now both the timeout and the verification use nanosecond precision.

This change also removes all uses of hamcres in this test file.

Fixes #200

Closing a Spanner client means that all resources that have been returned
by the client are no longer valid, including all DatabaseClients and
corresponding session pools. This will cause errors for any other process
that might still want to use these resources. This change marks when and by
which call stack a Spanner client is closed, and includes that in any
subsequent IllegalStateException that is returned to any process that tries
to use the resources that have been returned by the Spanner client. This
makes it easier to track down where and when a Spanner client is closed by
accident.

* fix: Partitioned DML timeout was not always respected

Setting a timeout value for Partitioned DML would not be respected if the timeout
value was higher than the timeout value set for the ExecuteSql RPC on the SpannerStub.
Lower timeout values would be respected.

Fixes #199

* fix: add ignored changes + InternalApi

* tests: add test for retry on UNAVAILABLE

…cies to v0.3.1 (#190)

🤖 I have created a release \*beep\* \*boop\* 
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### Updating meta-information for bleeding-edge SNAPSHOT release.
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This PR was generated with [Release Please](https://.com/googleapis/release-please).

The PartitionedDML stub was not closed when Spanner was closed.
In addition, Spanner did not wait for the channels to actually close,
causing some test cases to (sometimes) log a warning that the channel
had not been closed.

🤖 I have created a release \*beep\* \*boop\* 
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## [1.55.0](https://www..com/googleapis/java-spanner/compare/v1.54.0...v1.55.0) (2020-05-19)


### Features

* mark when a Spanner client is closed ([#198](https://www..com/googleapis/java-spanner/issues/198)) ([50cb174](https://www..com/googleapis/java-spanner/commit/50cb1744e7ede611758d3ff63b3df77a1d3682eb))


### Bug Fixes

* make it possible to override backups methods ([#195](https://www..com/googleapis/java-spanner/issues/195)) ([2d19c25](https://www..com/googleapis/java-spanner/commit/2d19c25ba32847d116194565e67e1b1276fcb9f8))
* Partitioned DML timeout was not always respected ([#203](https://www..com/googleapis/java-spanner/issues/203)) ([13cb37e](https://www..com/googleapis/java-spanner/commit/13cb37e55ddfd1ff4ec22b1dcdc20c4832eee444)), closes [#199](https://www..com/googleapis/java-spanner/issues/199)
* partitionedDml stub was not closed ([#213](https://www..com/googleapis/java-spanner/issues/213)) ([a2d9a33](https://www..com/googleapis/java-spanner/commit/a2d9a33fa31f7467fc2bfbef5a29c4b3f5aea7c8))
* reuse clientId for invalidated databases ([#206](https://www..com/googleapis/java-spanner/issues/206)) ([7b4490d](https://www..com/googleapis/java-spanner/commit/7b4490dfb61fbc81b5bd6be6c9a663b36b5ce402))
* use nanos to prevent truncation errors ([#204](https://www..com/googleapis/java-spanner/issues/204)) ([a608460](https://www..com/googleapis/java-spanner/commit/a60846043dc0ca47e1970d8ab99380b6d725c7a9)), closes [#200](https://www..com/googleapis/java-spanner/issues/200)


### Dependencies

* update dependency com.google.cloud:google-cloud-shared-dependencies to v0.3.1 ([#190](https://www..com/googleapis/java-spanner/issues/190)) ([ad41a0d](https://www..com/googleapis/java-spanner/commit/ad41a0d4b0cc6a2c0ae0611c767652f64cfb2fb7))
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This PR was generated with [Release Please](https://.com/googleapis/release-please).