test/lib/base: Reduce redundant build steps
test/lib/base: Reduce redundant build steps

Currently, the build steps of "go get" and removing the downloaded
directory are not effective steps.
For example, "go get" for downloading dependencies can be replaced
with "dep ensure".

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>

fujita/gobgp,a16/gobgp,a16/gobgp,fujita/gobgp,j-kato/gobgp,osrg/gobgp,fujita/gobgp,osrg/gobgp,a16/gobgp,j-kato/gobgp,tamihiro/gobgp,osrg/gobgp,tamihiro/gobgp,Dipsingh/gobgp,a16/gobgp,Dipsingh/gobgp,osrg/gobgp,a16/gobgp,a16/gobgp,fujita/gobgp,tamihiro/gobgp,j-kato/gobgp,a16/gobgp,tamihiro/gobgp,Dipsingh/gobgp