Add .travis.yml

Travis builders have maximum work time ~49 minutes,
so we have to use 5 builders and spread the ZTS over
them using test group tags.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: George Melikov <mail@gmelikov.ru>
Closes #6829