fs_mgr: Allow commas in boot device paths.

If the value of androidboot.boot_devices has a comma in its path, it'll
get split and /dev/block/by-name symlinks won't work. As a workaround,
add "androidboot.boot_device" as a valid command-line parameter. It can
be repeated multiple times to retain multiple-boot-device semantics.

Bug: 153024538
Test: device boots with androidboot.boot_device= set
Change-Id: I1be5aeec287ba198768c3452b1930d59b2f13463
diff --git a/fs_mgr/fs_mgr_fstab.cpp b/fs_mgr/fs_mgr_fstab.cpp
index a836d3b..b218f21 100644
--- a/fs_mgr/fs_mgr_fstab.cpp
+++ b/fs_mgr/fs_mgr_fstab.cpp
@@ -829,6 +829,20 @@
         return std::set<std::string>(boot_devices.begin(), boot_devices.end());
     }
 
+    std::string cmdline;
+    if (android::base::ReadFileToString("/proc/cmdline", &cmdline)) {
+        std::set<std::string> boot_devices;
+        const std::string cmdline_key = "androidboot.boot_device";
+        for (const auto& [key, value] : fs_mgr_parse_boot_config(cmdline)) {
+            if (key == cmdline_key) {
+                boot_devices.emplace(value);
+            }
+        }
+        if (!boot_devices.empty()) {
+            return boot_devices;
+        }
+    }
+
     // Fallback to extract boot devices from fstab.
     Fstab fstab;
     if (!ReadDefaultFstab(&fstab)) {