libbootloader_message: use different fstab paths for normal/recovery boot

libbootloader_message is used by both normal boot and recovery boot.
It needs to use different fstab paths, respectively. Otherwise, factory
reset will fail when we move /fstab.{ro.hardware} to /vendor/etc/.

  Recovery boot: fs_mgr_read_fstab_with_dt("/etc/recovery.fstab")
  Normal boot: fs_mgr_read_fstab_default()

Bug: 35811655
Bug: 36502022

Test: normal boot sailfish, go to Settings > System & tap on
      "Factory Data reset"
Test: recovery boot sailfish

Change-Id: I253f5bdfb9be8a01f80856eb1194f85cdf992bbd

bootloader_message/bootloader_message.cpp

@@ -19,6 +19,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <string>
 #include <vector>
@@ -30,8 +31,13 @@
 #include <fs_mgr.h>
 
 static std::string get_misc_blk_device(std::string* err) {
-  std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),
-                                                             fs_mgr_free_fstab);
+  std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(nullptr, fs_mgr_free_fstab);
+  // Use different fstab paths for normal boot and recovery boot, respectively
+  if (access("/sbin/recovery", F_OK) == 0) {
+    fstab.reset(fs_mgr_read_fstab_with_dt("/etc/recovery.fstab"));
+  } else {
+    fstab.reset(fs_mgr_read_fstab_default());
+  }
   if (!fstab) {
     *err = "failed to read default fstab";
     return "";