Read fstab from the source build.

When creating incremental OTAs, we should always use the fstab from the
source build instead of the target.

Bug: 21948974
Change-Id: I8b6a18f64b412f782184f9d382544ed0ce093fb4
(cherry picked from commit dd24da9ec91b74b7e3c8d1af9f1f9f792d41ac4d)
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 82d6313..531a728 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -832,9 +832,9 @@
   #    (allow recovery to mark itself finished and reboot)
 
   if OPTIONS.two_step:
-    if not OPTIONS.info_dict.get("multistage_support", None):
+    if not OPTIONS.source_info_dict.get("multistage_support", None):
       assert False, "two-step packages not supported by this build"
-    fs = OPTIONS.info_dict["fstab"]["/misc"]
+    fs = OPTIONS.source_info_dict["fstab"]["/misc"]
     assert fs.fs_type.upper() == "EMMC", \
         "two-step packages only supported on devices with EMMC /misc partitions"
     bcb_dev = {"bcb_dev": fs.device}
@@ -879,7 +879,8 @@
           GetBuildProp("ro.build.thumbprint", OPTIONS.source_info_dict))
 
   if updating_boot:
-    boot_type, boot_device = common.GetTypeAndDevice("/boot", OPTIONS.info_dict)
+    boot_type, boot_device = common.GetTypeAndDevice(
+        "/boot", OPTIONS.source_info_dict)
     d = common.Difference(target_boot, source_boot)
     _, _, d = d.ComputePatch()
     if d is None:
@@ -1218,9 +1219,9 @@
   #    (allow recovery to mark itself finished and reboot)
 
   if OPTIONS.two_step:
-    if not OPTIONS.info_dict.get("multistage_support", None):
+    if not OPTIONS.source_info_dict.get("multistage_support", None):
       assert False, "two-step packages not supported by this build"
-    fs = OPTIONS.info_dict["fstab"]["/misc"]
+    fs = OPTIONS.source_info_dict["fstab"]["/misc"]
     assert fs.fs_type.upper() == "EMMC", \
         "two-step packages only supported on devices with EMMC /misc partitions"
     bcb_dev = {"bcb_dev": fs.device}
@@ -1257,7 +1258,8 @@
 
     common.ZipWriteStr(output_zip, "patch/boot.img.p", d)
 
-    boot_type, boot_device = common.GetTypeAndDevice("/boot", OPTIONS.info_dict)
+    boot_type, boot_device = common.GetTypeAndDevice(
+        "/boot", OPTIONS.source_info_dict)
 
     script.PatchCheck("%s:%s:%d:%s:%d:%s" %
                       (boot_type, boot_device,