ast_coredumper: add Asterisk information dump

This patch makes it so ast_coredumper now outputs the following information to
a *-info.txt file when processing a core file:

  asterisk version and "built by" string
  BUILD_OPTS
  system start, and last reloaded date/time
  taskprocessor list
  equivalent of "bridge show all"
  equivalent of "core show channels verbose"

Also a slight modification was made when trying to obtain the pid(s) of a
running Asterisk. If it fails to retrieve any it now reports an error.

Change-Id: I54f35c19ab69b8f8dc78cc933c3fb7c99cef346b