fs_mgr: Allow remounts with Magisk installed

This allows remount to gracefully mount /system when Magisk
is installed.

As a sidenote, the ro.debuggable property check can safely
be removed due to the simple fact that CPP preprocessor flag
ALLOW_ADBD_DISABLE_VERITY=1 is passed when building
userdebug/eng.

Change-Id: Ic10eccbf5d225468c3dc42f8ae3ae7c05b49a699

fs_mgr/fs_mgr_remount.cpp

@@ -150,7 +150,7 @@ static int do_remount(int argc, char* argv[]) {
     // If somehow this executable is delivered on a "user" build, it can
     // not function, so providing a clear message to the caller rather than
     // letting if fall through and provide a lot of confusing failure messages.
-    if (!ALLOW_ADBD_DISABLE_VERITY || (android::base::GetProperty("ro.debuggable", "0") != "1")) {
+    if (!ALLOW_ADBD_DISABLE_VERITY) {
         LOG(ERROR) << "only functions on userdebug or eng builds";
         return NOT_USERDEBUG;
     }
@@ -438,7 +438,8 @@ static int do_remount(int argc, char* argv[]) {
         fs_mgr_set_blk_ro(blk_device, false);
 
         // Find system-as-root mount point?
-        if ((mount_point == "/system") && !GetEntryForMountPoint(&mounts, mount_point) &&
+        if ((mount_point == "/system" || mount_point == "/system_root") &&
+            !GetEntryForMountPoint(&mounts, mount_point) &&
             GetEntryForMountPoint(&mounts, "/")) {
             mount_point = "/";
         }