Spurious precondition failures caused by ifGenerationMatch preserved across save() calls

Blocked

• https://github.com/googleapis/gcs-resumable-upload/pull/243
• https://github.com/googleapis/gcs-resumable-upload/pull/244

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I’m using file('example', { generation: 0 }).save() and discovered a strange behavior. I’ve managed to get resumable saves stuck in my config store, and as a result, when I subsequently invoke file('example').save(), the ifGenerationMatch header is still present on the response.

This is caused by the resumable upload code, which is turned on by default. I’m not sure whether the bug is here or in that library.

Steps to reproduce:

const bucket = new Storage({ projectId }).bucket(bucketName)

await bucket.file('example').save('hello', { resumable: false })

try {
  await bucket.file('example', { generation: 0 }).save('hello')
} catch (e) {
  // Catch a precondition failure
}

// Saves a new version as expected.
await bucket.file('example').save('hello', { resumable: false })

// Expected to save a new version, but throws precondition failure
await bucket.file('example').save('hello')

[stephenplusplus]

I have sent a PR: https://github.com/googleapis/gcs-resumable-upload/pull/243

[stephenplusplus]

And a PR to expose uploadInstance.deleteConfig(): https://github.com/googleapis/gcs-resumable-upload/pull/244. This will have to be re-exposed through the Storage API after it ships in gcs-resumable-upload.