Switch to containerized environment for Travis CI

Original (virtualized) environment led to a test failure not
reproducible in development. Containerized CI builds permit debugging
and troubleshooting on local development machines via Docker.

.travis.yml

@@ -1,6 +1,5 @@
 dist: trusty
-sudo: required
-group: deprecated
+sudo: false
 notifications:
   email:
     - me+tv@zammad.com
@@ -11,6 +10,31 @@ addons:
   postgresql: "9.4"
   apt:
     packages:
+    - curl
+    - git-core
+    - patch
+    - build-essential
+    - bison
+    - zlib1g-dev
+    - libssl-dev
+    - libxml2-dev
+    - sqlite3
+    - libsqlite3-dev
+    - autotools-dev
+    - libxslt1-dev
+    - libyaml-0-2
+    - autoconf
+    - automake
+    - libreadline6-dev
+    - libyaml-dev
+    - libtool
+    - libgmp-dev
+    - libgdbm-dev
+    - libncurses5-dev
+    - pkg-config
+    - libffi-dev
+    - libmysqlclient-dev
+    - postfix
     - mysql-server-5.6
     - mysql-client-core-5.6
     - mysql-client-5.6
@@ -22,8 +46,6 @@ rvm:
   - 2.4.2
 before_install:
   - git fetch --unshallow
-  - sudo apt-get -qq update
-  - sudo apt-get install -y curl git-core patch build-essential bison zlib1g-dev libssl-dev libxml2-dev libxml2-dev sqlite3 libsqlite3-dev autotools-dev libxslt1-dev libyaml-0-2 autoconf automake libreadline6-dev libyaml-dev libtool libgmp-dev libgdbm-dev libncurses5-dev pkg-config libffi-dev libmysqlclient-dev postfix
   - if [ "${DB}" = "mysql" ]; then mysql -u root -e "CREATE USER 'some_user'@'localhost' IDENTIFIED BY 'some_pass';"; fi
   - if [ "${DB}" = "mysql" ]; then mysql -u root -e "GRANT ALL PRIVILEGES ON *.* TO 'some_user'@'localhost';"; fi
   - if [ "${DB}" = "mysql" ]; then cp config/database.yml.test-mysql config/database.yml; fi