snap: 0.x: prevent user site package conflicts (#3879)

* snap: restrict site-package checks

Fixes #3514

* debug commit

* sync master, revert debug

.travis.yml

@@ -106,6 +106,7 @@ jobs:
     - sudo /snap/bin/lxd.migrate -yes
     - sudo /snap/bin/lxd waitready
     - sudo /snap/bin/lxd init --auto
+    - git fetch --tags
     script:
     - ./scripts/build_snap.sh
     after_failure:

scripts/ci/before_install.sh

@@ -15,7 +15,7 @@ fi
 
 echo >env.sh
 
-if [[ "$TRAVIS_BUILD_STAGE_NAME" == "Test" ]]; then
+if [[ "$TRAVIS_BUILD_STAGE_NAME" == "test" ]]; then
   if [[ "$TRAVIS_OS_NAME" != "windows" ]]; then
     # NOTE: ssh keys for ssh test to be able to ssh to the localhost
     ssh-keygen -t rsa -N "" -f mykey
@@ -52,7 +52,11 @@ elif [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
 fi
 
 if [[ -n "$TRAVIS_TAG" ]]; then
-  echo "export SNAP_CHANNEL=stable" >>env.sh
+  if [[ $(echo "$TRAVIS_TAG" | grep -E '^[0-9]+\.[0-9]+\.[0-9]+$') ]]; then
+    echo "export SNAP_CHANNEL=stable" >>env.sh
+  else
+    echo "export SNAP_CHANNEL=beta" >>env.sh
+  fi
 else
   echo "export SNAP_CHANNEL=edge" >>env.sh
 fi

snap/snapcraft.yaml

@@ -29,7 +29,7 @@ parts:
     - git
     override-pull: |
         snapcraftctl pull
-        snapcraftctl set-version `cd $SNAPCRAFT_PART_SRC && git describe --tags`
+        snapcraftctl set-version $(cd $SNAPCRAFT_PART_SRC && git describe --tags)
         git diff --quiet || error_dirty_build
         echo 'PKG = "snap"' > $SNAPCRAFT_PART_SRC/dvc/utils/build.py
         # install all optional extras
@@ -38,6 +38,9 @@ parts:
         sed -rin 's/.*git.*diff.*--quiet.*//' $SNAPCRAFT_PART_SRC/dvc/version.py
     override-build: |
         snapcraftctl build
+        # prevent user site packages interfering with this snap - reference:
+        # https://github.com/snapcore/snapcraft/blob/19393ef36cd773a28131cec10cc0bfb3bf9c7e77/tools/snapcraft-override-build.sh#L18
+        sed -ri 's/^(ENABLE_USER_SITE = )None$/\1False/' $SNAPCRAFT_PART_INSTALL/usr/lib/python*/site.py
         cp $SNAPCRAFT_PART_BUILD/scripts/completion/dvc.bash $SNAPCRAFT_PART_INSTALL/completion.sh
 apps:
   dvc: