* Updated test_uuid.c to test the new API call.

* Made system use the new API call to eliminate "10's of lines" where
used.

* Fixed untested ast_strdup() return in stasis_subscribe() by eliminating
the need for it.  struct stasis_subscription now contains the uniqueid[]
string.

* Fixed some issues in exchangecal_write_event():
  Create uid with enough space for a UUID string to avoid a realloc.
  Fix off by one error if the calendar event provided a UUID string.
  There is no need to check for NULL before calling ast_free().


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@384302 65c4cc65-6c06-0410-ace0-fbb531ad65f3

git-svn-id: https://origsvn.digium.com/svn/asterisk/team/mmichelson/threadpool@377879 65c4cc65-6c06-0410-ace0-fbb531ad65f3

This provides a common API for dealing with unique identifiers.
The API provides methods to create, parse, copy, and stringify UUIDs.

An accompanying unit test is provided that tests all operations.

(closes issue ASTERISK-20726)
reported by Matt Jordan

Review: https://reviewboard.asterisk.org/r/2217



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@377846 65c4cc65-6c06-0410-ace0-fbb531ad65f3