Make AnalyticsSettings.salt respect disc content

When multipe JVM is running and both try to generate a salt value, the
content would diverge. This change makes the latter one read the content
of the disk so it will respect the value written previously.

Bug: 145560287
Test: unit test
Change-Id: I76c7556f0adc29ef883ab6f65c2a0a0086ba4f79
2 files changed