Linux translate: Print status once

[EricEdens]

At the end of Linux translation, statuses are double printed, once by Python and once by Bash. If Python reports a failure, but fails to flush its logs, then the incorrect status can be read by Daisy.

This was observed recently in the "Incorrect OS specified" test:

 startup-script-url: TranslateStatus: <serial-output key:'detected_distro' value:'debian'>
 startup-script-url: TranslateStatus: <serial-output key:'detected_major_version' value:'9'>
 startup-script-url: TranslateStatus: <serial-output key:'detected_minor_version' value:'12'>
 startup-script-url: TranslateDebug: Traceback (most recent call last):
 startup-script-url:   File "/usr/local/lib/python3.7/dist-packages/utils/common.py", line 246, in RunTranslate
 startup-script-url:     translate_func()
 startup-script-url:   File "/usr/local/lib/python3.7/dist-packages/translate.py", line 320, in translate
 startup-script-url:     release = _get_release(g)
 startup-script-url:   File "/usr/local/lib/python3.7/dist-packages/translate.py", line 162, in _get_release
 startup-script-url:     product, major, minor, supported))
 startup-script-url: ValueError: Import of debian-9.12 is not supported. The following versions are supported: [opensuse-15.1|2, sles-15.1|2, sles-12.4|5]
 startup-script-url: 
 startup-script-url: TranslateFailed: error: Import of debian-9.12 is not supported. The following versions are supported: [opensuse-15.1|2, sles-15.1|2, sles-12.4|5]
 startup-script-url: + NotifyExit
 startup-script-url: + [ 0 -eq 0 ]
 startup-script-url: + logger -p daemon.info TranslateSuccess: exits with return code 0
Nov 12 13:30:33 inst-translator-import-image-gzzm6 root: TranslateSuccess: exits with return code 0
 startup-script-url exit status 0
 Finished running startup scripts.

This PR disables Bash's final-status printing for Linux translations (except if there's a failure prior to running the Python interpreter).

Testing

• Ran the tests cli_tools_tests/e2e/gce_image_import_export/test_suites/import/import_tests.go

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dntczdx, EricEdens, zoran15

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[EricEdens]

/hold (We're preparing a release, scheduled to ship Thursday)

[EricEdens]

/unhold: Talked with Zach, and we're delaying the release until after Thanksgiving