Migrate hashtest/hashtest2 to be unit tests.

Migrate hashtest/hashtest2 to be unit tests.

Both hashtest and hashtest2 are manual testing apps that thrash hash
tables (hashtab and ao2 containers, respectively), by spinning up
several threads that randomly insert, delete, lookup and iterate over
the hash table. If the app doesn't crash, the hash table probably passes
the test. Those utils are not a part of the typical Asterisk build, so
they do not usually get compiled. This all makes them less that useful.

This patch removes those manual test programs and replaces them with
Asterisk unit test modules (test_{hashtab,astobj2}_thrash.so). It also
attempts to make the tests more deterministic.

* Rather than spinning up some number of threads that operate on the
  hash table randomly, spin up four threads that concurrenly add,
  remove, lookup and iterate over the hash table.
* Each thread checks the state of the hash table both during and after
  execution, and indicates a test failure if things are not as expected.
* Each thread times out after 60 seconds to prevent deadlocking the unit
  test run.

(closes issue ASTERISK-20505)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2189/
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Merged revisions 376306 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 376315 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@376339 65c4cc65-6c06-0410-ace0-fbb531ad65f3