Make storage dirs remount fork() safe

Also, use the pids provided by system server to remount all existing
processes, so we don't need to do the heavy and unreliable scanning in
/proc anymore.

Bug: 149548518
Test: atest AdoptableHostTest
Change-Id: Ifb5b79a3bc5438f36e0d61ec8aec96bdbc60ca13
diff --git a/model/EmulatedVolume.h b/model/EmulatedVolume.h
index 12d01ec..b25fb7c 100644
--- a/model/EmulatedVolume.h
+++ b/model/EmulatedVolume.h
@@ -41,6 +41,7 @@
     EmulatedVolume(const std::string& rawPath, dev_t device, const std::string& fsUuid, int userId);
     virtual ~EmulatedVolume();
     std::string getRootPath() const override;
+    bool isFuseMounted() const { return mFuseMounted; }
 
   protected:
     status_t doMount() override;