Installd: Introduce otapreopt

Add a tool for dexopt during OTA. The tool will use /data/ota as
an ANDROID_ROOT wrt/ the dalvik-cache, compiling a new boot image
and system apps into this directory. Other apps will be compiled
to odex files suffixed with ".b".

Bug: 25612095
Change-Id: I6ac382973f13850f6b37402a1b2330c0014b47d9