[LTP] [PATCH 3/3] travis: Use docker based builds

[Petr Vorel]

Hi,

Proposed docker based build in travis:
https://travis-ci.org/pevik/ltp/builds/470037766

Compare with previous Trusty based build:
https://travis-ci.org/linux-test-project/ltp/builds/469670856


Kind regards,
Petr