twrp: use ANDROID_ROOT environment variable

instead of hard-coded /system path

I updated most of the references I found,
but there might be more

For devices that have to mount system at /system_root,
this allows system to be bind mounted to /system
and detected properly by TWRP

Change-Id: I9f142fd8cec392f5b88e95476258dab9c21a9aac
diff --git a/openrecoveryscript.cpp b/openrecoveryscript.cpp
index d7e4a23..86c90a6 100644
--- a/openrecoveryscript.cpp
+++ b/openrecoveryscript.cpp
@@ -147,8 +147,8 @@
 				// Wipe
 				if (strcmp(value, "cache") == 0 || strcmp(value, "/cache") == 0) {
 					PartitionManager.Wipe_By_Path("/cache");
-				} else if (strcmp(value, "system") == 0 || strcmp(value, "/system") == 0) {
-					PartitionManager.Wipe_By_Path("/system");
+				} else if (strcmp(value, PartitionManager.Get_Android_Root_Path().c_str()) == 0 || strcmp(value, PartitionManager.Get_Android_Root_Path().c_str()) == 0) {
+					PartitionManager.Wipe_By_Path(PartitionManager.Get_Android_Root_Path());
 				} else if (strcmp(value, "dalvik") == 0 || strcmp(value, "dalvick") == 0 || strcmp(value, "dalvikcache") == 0 || strcmp(value, "dalvickcache") == 0) {
 					PartitionManager.Wipe_Dalvik_Cache();
 				} else if (strcmp(value, "data") == 0 || strcmp(value, "/data") == 0 || strcmp(value, "factory") == 0 || strcmp(value, "factoryreset") == 0) {
@@ -667,14 +667,14 @@
 
 int OpenRecoveryScript::remountrw(void)
 {
-	bool remount_system = PartitionManager.Is_Mounted_By_Path("/system");
+	bool remount_system = PartitionManager.Is_Mounted_By_Path(PartitionManager.Get_Android_Root_Path());
 	int op_status;
 	TWPartition* Part;
 
-	if (!PartitionManager.UnMount_By_Path("/system", true)) {
+	if (!PartitionManager.UnMount_By_Path(PartitionManager.Get_Android_Root_Path(), true)) {
 		op_status = 1; // fail
 	} else {
-		Part = PartitionManager.Find_Partition_By_Path("/system");
+		Part = PartitionManager.Find_Partition_By_Path(PartitionManager.Get_Android_Root_Path());
 		if (Part) {
 			DataManager::SetValue("tw_mount_system_ro", 0);
 			Part->Change_Mount_Read_Only(false);