move snap build code

.travis.yml

@@ -11,6 +11,7 @@ before_script:
   # Use Travis retry feature for farm tests since they are flaky
   - 'if [[ "$TOXENV" == "travis-test-farm"* ]]; then export TRAVIS_RETRY=travis_retry; fi'
   - export TOX_TESTENV_PASSENV=TRAVIS
+  - 'if [[ "$SNAP" == true ]]; then snap/local/build_and_install.sh; fi'
 
 # Only build pushes to the master branch, PRs, and branches beginning with
 # `test-`, `travis-test-`, or of the form `digit(s).digit(s).x`. This reduces
@@ -224,14 +225,7 @@ matrix:
             - libaugeas0
       <<: *extended-test-suite
     - sudo: required
-      env: TOXENV=integration-external,apacheconftest-external-with-pebble
-      before_install:
-        - sudo /snap/bin/lxd.migrate -yes
-        - sudo /snap/bin/lxd waitready
-        - sudo /snap/bin/lxd init --auto
-        - tools/strip_hashes.py letsencrypt-auto-source/pieces/dependency-requirements.txt > constraints.txt
-        - sudo snapcraft --use-lxd
-        - sudo snap install --dangerous --classic *.snap
+      env: SNAP=true TOXENV=integration-external,apacheconftest-external-with-pebble
       addons:
         snaps:
           - name: snapcraft

snap/local/build_and_install.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+set -ex
+
+sudo /snap/bin/lxd.migrate -yes
+sudo /snap/bin/lxd waitready
+sudo /snap/bin/lxd init --auto
+tools/strip_hashes.py letsencrypt-auto-source/pieces/dependency-requirements.txt > constraints.txt
+sudo snapcraft --use-lxd
+sudo snap install --dangerous --classic *.snap