M52 master builder had issue for finding username while updating manifest-versions.

It seems to have the same symptom as  issue 592553 , which also happened on master builder about 2 months ago:
https://bugs.chromium.org/p/chromium/issues/detail?id=592553&can=1

According to master build history, it happened sometimes, but not continuously.
https://uberchromegw.corp.google.com/i/chromeos/builders/master-release?numbuilds=50


Log snippets:
17:30:13: INFO: Updating manifest-versions checkout.
17:30:18: WARNING: Could not update manifest-versions checkout.
17:30:18: INFO: Cloning fresh manifest-versions checkout.
17:30:30: ERROR: Failed to update the status for master-release with the following error cwd=/b/cbuild/internal_master/manifest-versions-internal
17:30:30: ERROR: Retrying to generate buildspec:  Retry 1/20
17:30:30: INFO: No manifest-versions checkout exists at /b/cbuild/internal_master/manifest-versions-internal
......
RunCommandError: return code: 128; command: git clone https://chrome-internal.googlesource.com/chromeos/manifest-versions /b/cbuild/internal_master/manifest-versions-internal
Cloning into '/b/cbuild/internal_master/manifest-versions-internal'...
fatal: could not read Username for 'https://chrome-internal.googlesource.com': No such device or address

Full log:
https://uberchromegw.corp.google.com/i/chromeos/builders/master-release/builds/1992/steps/CanaryCompletion/logs/stdio



And I think it also caused some PFQ/CQ build failure and branch build failures.

PFQ log snippets:
@@@STEP_FAILURE@@@
20:30:47: ERROR: <type 'exceptions.IOError'>: [Errno 2] No such file or directory: '/b/cbuild/internal_master/manifest-versions-internal/chrome-LKGM-candidates/buildspecs/52/8278.0.0-rc1.xml'
......
IOError: [Errno 2] No such file or directory: '/b/cbuild/internal_master/manifest-versions-internal/chrome-LKGM-candidates/buildspecs/52/8278.0.0-rc1.xml'

PFQ failure:
https://uberchromegw.corp.google.com/i/chromeos/builders/amd64-generic-chromium-pfq/builds/8585/steps/MasterSlaveLKGMSync/logs/stdio
https://uberchromegw.corp.google.com/i/chromeos/builders/daisy-chromium-pfq/builds/8501/steps/MasterSlaveLKGMSync/logs/stdio
https://uberchromegw.corp.google.com/i/chromeos/builders/peach_pit-chrome-pfq/builds/2001/steps/MasterSlaveLKGMSync/logs/stdio

and others...