adb-remount-test: Miscellaneous fixes - 2nd round

* Call adb_wait in adb_reboot, as virtually all adb_reboot callsites are
  immediately followed by adb_wait.
* Remove |data| option from skip_administrative_mounts. The |data|
  option doesn't really work anyway, because vold & init creates
  bewildering heirarchy of /data bind-mounts, so it's not feasible to
  filter /data by mountpoints. It's more sensible to filter by the /data
  device node name, which should be done by the caller.
* Untangle skip_administrative_mounts and skip_unrelated_mounts.
  I don't know why we need two separate functions that do similar
  things. Just merge them together.

Bug: 243116800
Test: adb-remount-test
Change-Id: I847f0b8cc2a952bb4c8656a43da783f312670061