Compilation fix for protocol plugin app on Ubuntu14.10

Compilation fix for protocol plugin app on Ubuntu14.10

Compilation of mqtt sample app was failing as pthread was included in
LIBS but should be appended after connectivity_abstraction as it depends on the pthread library.

Change-Id: Ie1019c5ba4b31a06f7e25a3e2ce338ea21c91b52
Signed-off-by: Habib Virji <habib.virji@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/881
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Younghyun Joo <yh_.joo@samsung.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>