Add ASTSBINDIR to the list of configurable paths

This patch also makes astdb2sqlite3 and astcanary use the configured
directory instead of relying on $PATH.

(closes issue ASTERISK-18959)
Review: https://reviewboard.asterisk.org/r/1613/
........

Merged revisions 347344 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@347345 65c4cc65-6c06-0410-ace0-fbb531ad65f3