Fix tools test

This changes the test to no longer reference $GOPATH. Instead, it
removes `github.com/osrg/gobgp/` fore calling grep from the package
name before calling grep so that it greps a location relative to
wherever the script was located when it was called. This should work
regardless of $GOPATH.

The problem was that in a Travis CI run, the repository is not cloned
to the correct spot under $GOPATH and the grep fails because it is
looking in the wrong place. The repository is cloned to
`/home/travis/build/osrg/gobgp` and GOPATH is set to
`/home/travis/gopath` during a Travis run which don't match up.

tools/grep_avoided_functions.sh

@@ -9,14 +9,17 @@ FUNCS=(
 )
 
 SCRIPT_DIR=`dirname $0`
+cd "${SCRIPT_DIR}/.."
 
 RESULT=0
 
+PKG_BASE=github.com/osrg/gobgp
+
 for FUNC in ${FUNCS[@]}
 do
-    for GO_PKG in $(go list github.com/osrg/gobgp/... | grep -v '/vendor/')
+    for GO_PKG in $(go list $PKG_BASE/... | grep -v '/vendor/')
     do
-        grep ${FUNC} -r ${GOPATH}/src/${GO_PKG}
+        grep ${FUNC} -r ${GO_PKG#$PKG_BASE/}
         if [ $? -ne 1 ]
         then
             RESULT=1