Maybe fix issue #17969789: Shamu FR: Runtime restart while scrolling Instagram

It looks like there were a couple problems in the code:

- It would not 0-terminate the string it read, to make sure we didn't
  see garbage at the end.
- It didn't reduce buf_len as it processes data in the buffer, so if
  we need to read more we will increase the buffer length to be longer
  than the actual available data.

Also put in some logs about every thing we kill, so we can see what
is going on when debugging.  And add a special check for us trying
to kill pid 0 for any reason, since doing so seem to be terminal to
the caller.

Change-Id: I2fe29bfef08938b8a2eb182475c0705c14d8d84f