{Docker,Jenkins}file: update go version 1.13.4

When go modules enabled user code is not intended be in GOROOT(/go) hence
placing source code in /src. Otherwise we hit with below error:

go: inconsistent vendoring in /go/src/github.com/intel/pmem-csi:
        go.mod requires github.com/intel/pmem-csi  but vendor/modules.txt does not include it.
        run 'go mod tidy; go mod vendor' to sync
make: *** [Makefile:70: pmem-csi-driver] Error 1

Ref: golang/go#34657

Jenkinsfile: Place the pmem-csi source out of GOPATH

.dockerignore

@@ -8,3 +8,5 @@
 ! test/test-config.sh
 ! hack/copy-modules-license.sh
 ! vendor/**
+! go.mod
+! go.sum

Dockerfile

@@ -18,7 +18,7 @@ ARG SWUPD_UPDATE_ARG
 ARG NDCTL_VERSION="67"
 ARG NDCTL_CONFIGFLAGS="--disable-docs --without-systemd --without-bash"
 ARG NDCTL_BUILD_DEPS="os-core-dev devpkg-util-linux devpkg-kmod devpkg-json-c"
-ARG GO_VERSION="1.12.9"
+ARG GO_VERSION="1.13.4"
 
 #pull dependencies required for downloading and building libndctl
 ARG CACHEBUST
@@ -78,11 +78,9 @@ FROM build as binaries
 
 # build pmem-csi-driver
 ARG VERSION="unknown"
-# Beware that this copying is filtered with .dockerignore!
-ADD . /go/src/github.com/intel/pmem-csi
-ENV GOPATH=/go
+ADD . /src/pmem-csi
 ENV PKG_CONFIG_PATH=/usr/lib/pkgconfig/
-WORKDIR /go/src/github.com/intel/pmem-csi
+WORKDIR /src/pmem-csi
 ARG BIN_SUFFIX
 # Here we choose explicitly which binaries we want in the image and in
 # which flavor (production or testing). The actual binary name in the

Jenkinsfile

@@ -48,7 +48,8 @@ pipeline {
         /* last version before the 1.14 update in 28630 */
         CLEAR_LINUX_VERSION_1_13 = "28620"
 
-        PMEM_PATH = "/go/src/github.com/intel/pmem-csi"
+        // path for placing the source to build outside of GOROOT
+        PMEM_PATH = "/src/pmem-csi"
         REGISTRY_NAME = "cloud-native-image-registry.westus.cloudapp.azure.com"
 
         // Per-branch build environment, marked as "do not promote to public registry".