odrefresh: support --zygote-arch in target variant

The new flag will override the value from ro.zygote.

Bug: 205750213
Test: odrefresh completes in the VM with hacks, with ro.zygote. With
      this change, odrefresh can still complete without ro.zygote.
Change-Id: I1bbf7d9a09b5e4ba60ebcd23384f1ad2b52ea668
1 file changed