odrefresh: Add --staging-dir

Staging directory provides an alternative output directory to what
PaletteCreateOdrefreshStagingDirectory returns.

My first attempt was actually to make
PaletteCreateOdrefreshStagingDirectory respect ART_APEX_DATA, but the
function as a stable API has to return a static C pointer. Instead of
using a global variable to store the path, this flag is added instead,

Bug: 206468124
Test: atest odsign_e2e_tests
Test: atest art_standalone_odrefresh_tests
Test: atest ComposHostTestCases
Change-Id: I4e8091890a76b09a5b85ca520f9973c20100a47a
diff --git a/odrefresh/odrefresh_main.cc b/odrefresh/odrefresh_main.cc
index cd16e9c..315e898 100644
--- a/odrefresh/odrefresh_main.cc
+++ b/odrefresh/odrefresh_main.cc
@@ -239,6 +239,8 @@
       config->SetMaxChildProcessSeconds(seconds);
     } else if (ArgumentMatches(arg, "--zygote-arch=", &value)) {
       zygote = value;
+    } else if (ArgumentMatches(arg, "--staging-dir=", &value)) {
+      config->SetStagingDir(value);
     } else if (!InitializeCommonConfig(arg, config)) {
       UsageError("Unrecognized argument: '%s'", arg);
     }