apexd: Create top-level /data/apex folders at boot

- package manager needs to read from /data/apex/active, hence 0750
- both /data/apex/backups and /data/apex/sessions are internal to apexd,
  hence 0700

Bug: 123927167
Fixes: 123927167
Test: apex_e2e_tests, flashall -w & checked folders were created
Change-Id: I06c28328afe4945d082acd890401651bd37fcb20