Move tzdatacheck execution after apex is mounted

tzdatacheck references files in the runtime apex so should
not be executed before the apex mounts are ready.

Test: Manual tests (see b/123270813); observed tzdatacheck running after
      apex files are mounted
Bug: 123270813
Bug: 116191025
Bug: 119293618
Bug: 113373927
Change-Id: I249d127c1d568bc5025d81b0bb4187c81363d897