clang compiler warnings: Fix various warnings for tests

This patch fixes a variety of clang compiler warnings for unit tests. This
includes autological comparison issues, ignored return values, and
interestingly enough, one embedded function. Fun!

Review: https://reviewboard.asterisk.org/r/4555

ASTERISK-24917
Reported by: dkdegroot
patches:
  rb4555.patch submitted by dkdegroot (License 6600)
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Merged revisions 434705 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 434706 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@434707 65c4cc65-6c06-0410-ace0-fbb531ad65f3