Move boot color sysprop parsing to after loading zips.

Otherwise the sysprops would not be loaded yet and accessing them would
return empty strings.

Though unlikely, this is not 100% safe because boot color sysprops
are not guaranteed to be loaded by the time zips are loaded. A TODO
here is to understand boot steps and their timing implications so
that we can fully avoid the race condition.

Bug: 190093578
Test: adb shell setprop persist.bootanim.color(1-4), then reboot phone.
Change-Id: I603da080b1732a436a10dbaca6f2be9f158124dc