Set correct install times for system user

The firstInstallTime and lastUpdateTime for the system user was being
set to the currentTime if the firstInstallTime is 0 when scaning
non-system package during device boot. This resulted in the
firstInstallTime and lastUpdateTime incorrectly to be set to the
currentTime even when the package was already installed earlier for
another user. Fixed this to only set the firstInstallTime and
lastUpdateTime if the earliestFirstInstallTime is 0.

Additionally set the firstInstallTime in commitPackagesLocked when
setting the lastUpdateTime when replacing a packge. This should result
in correctly setting the firstUpdateTime when installing a existing
package for a different user.

Bug: 360751150
Test: atest AppMetadataTest
Flag: EXEMPT bug fix
Change-Id: Ibb809611c8cd63709d1844a94137d628174aaf29