docs: Use DPDK 17.05.2 release.

docs: Use DPDK 17.05.2 release.

Modify docs and travis linux build script to use the DPDK 17.05.2
release branch to benefit from most recent bug fixes.

There are no new features introduced in the DPDK release, only back
ported bug fixes. For completeness these bug fixes have been documented
under the 17.05.2 section in the link below.

http://dpdk.org/doc/guides-17.05/rel_notes/release_17_05.html

Signed-off-by: Ian Stokes <ian.stokes@intel.com>
Signed-off-by: Darrell Ball <dlu998@gmail.com>