Mark apexd session as successful before marking staged session applied

Failing to mark session as successful won't block this staged session:
- it's mostly for bookkeeping purposes, in the future apexd might just
  delete information about the session after it is marked as successful;
- in case this call failed, when new session is staged apexd will delete
  all dangling sessions.

Bug: 124215327
Fixes: 124215327
Test: apex_e2e_tests
Change-Id: I7c9a068bc32352792610e7190e08a884bb5d09a5