e2fsdroid: support multiple selinux file contexts

Support passing a string of multiple selinux file contexts separated by
comma with -S option.

E.g. e2fsdroid -S ctx1,ctx2 output

Test: make systemimage
Bug: 35219933
Change-Id: Icc0f9d5d6180b5db7d68f7de45a1128f5a20be89
3 files changed