DynamicSystemInstallationService: Support remount for DSU guest system

DSU service would try to install a DSU scratch partition if host system
is debuggable.
If the scratch partition failed to install, then skip installing
scratch, as remount support should be optional.
Otherwise if the guest system is non-debuggable, then the scratch
partition would be ignored by guest, which is harmless.
Otherwise the guest system is debuggable, which means the guest system
would be able to do adb remount.

Relax partition allocation status polling rate from 10ms -> 100ms,
because there's no point polling faster than the screen framerate.

Bug: 165925766
Test: TH
Test: Install a DSU system on a debuggable host, reboot into the guest
  system, and guest system can remount.
Change-Id: I9a8255483cc963ebcf7a2909e68ac69371cb369f