Do not stream output in acceptance tests

[shreyas-goenka]

Changes

Instead of printing output logs line by line, now we'll store the entire output in memory before writing it to a file.

Why

Calling multiple write operations using the FUSE mount for the workspace file system seems to leave the file system in an inconsistent state, with reads not returning recent writes.

Using a single write operation seems to workaround that issue. This PR does so to enable DBR testing.

Note: I've been unable to reproduce the FUSE bug outside of the acceptance testing framework.

Tests

Existing tests pass. One test was updated to reflect that output.txt is not created immediately as the process is running.

[eng-dev-ecosystem-bot]

Run: 17377223671

	Env	✅​pass	🔄​flaky	🙈​skip
✅​	aws linux	308		509
✅​	aws windows	309		508
🔄​	aws-ucws linux	416	4	407
🔄​	aws-ucws windows	420	1	406
✅​	azure linux	308		508
✅​	azure windows	309		507
✅​	azure-ucws linux	420		406
✅​	azure-ucws windows	421		405
✅​	gcp linux	307		510
✅​	gcp windows	308		509

Test Name	aws-ucws linux	aws-ucws windows
TestAccept	🔄​flaky	✅​pass
TestAccept/bundle/deployment/bind/dashboard	🔄​flaky	✅​pass
TestAccept/bundle/deployment/bind/dashboard/recreation	🔄​flaky	✅​pass
TestDashboardAssumptions_WorkspaceImport	🔄​flaky	🔄​flaky

[shreyas-goenka]

I've filed the FUSE consistency issue with the files team. I'm putting this PR on hold until we have some clarity from their side.

[github-actions[bot]]

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