Track hostapd's life via pid files

init now writes hostapd's pid to a file.  We can use
this information to check if there is a process that looks
like hostapd running.

Bug: 30311493
Change-Id: I3ad24b5fa70ae963c1aa0d4b1c11d00f60dff8d1
Test: with a patch to wificond, hostapd starts and stops reliably on bullhead
2 files changed
tree: 5d73b8ece2ea69863943b7e20bd713801aec10c1
  1. libwifi_hal/
  2. libwifi_system/
  3. service/
  4. tests/