fixed go module in GSKY docker build (#524)

Author: edisonguo

docker/build_gsky.sh

@@ -7,28 +7,20 @@ C_INCLUDE_PATH=$(nc-config --includedir)
 export C_INCLUDE_PATH
 
 wget -q -O go.tar.gz https://dl.google.com/go/go1.16.3.linux-amd64.tar.gz
-tar -xf go.tar.gz
+rm -rf go && tar -xf go.tar.gz && rm -f go.tar.gz
 
-mkdir /gopath
 export GOROOT=/go
-export GOPATH=/gopath
+export GOPATH=/gsky/gopath
 export PATH="$PATH:$GOROOT/bin"
 
-(set -xeu
-go get github.com/nci/gsky
-if [ "$gsky_repo" != "$DEFAULT_GSKY_REPO" ]
-then
-  rm -rf $GOPATH/src/github.com/nci/gsky
-  git clone "$gsky_repo" $GOPATH/src/github.com/nci/gsky
-fi
+rm -rf $GOPATH && mkdir $GOPATH
+git clone "$gsky_repo" $GOPATH/src/github.com/nci/gsky
 
+(set -xeu
 cd $GOPATH/src/github.com/nci/gsky
 
 mkdir -p /gsky
 ./configure --prefix=/gsky --bindir=/gsky/bin --sbindir=/gsky/bin --libexecdir=/gsky/bin
 make all
 make install
 )
-
-rm -f go.tar.gz
-rm -rf gopath