[RFC PATCH 1/6] travis.yml: Bump default environment to Ubuntu Bionic

[Wainer dos Santos Moschetta <wainersm@redhat.com>]

Currently some KVM tests are skipped because Travis' Ubuntu 16.04 (Xenial)
does not provide nested virtualization (unlike Travis' Ubuntu 18.04). So
this switch the default job environment from Ubuntu Xenial to 18.04 (Bionic).

Notes:

1. The Ubuntu Bionic's libssh-dev package has a bug [1] that prevents QEMU
  from being built with ssh support. Therefore, the libssh-dev is not even
  installed in the job environment until a fix is not shipped.

  [1] https://bugs.launchpad.net/qemu/+bug/1838763

2. The '[aarch64] GCC check-tcg' and '[ppc64] GCC check-tcg' jobs
  explicitly use Xenial so they aren't converted on this patch.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
---
 .travis.yml | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index 5887055951..e46c44bbee 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,7 @@
-# The current Travis default is a VM based 16.04 Xenial on GCE
+# The current Travis default is a VM based 18.04 Xenial on GCE
 # Additional builds with specific requirements for a full VM need to
 # be added as additional matrix: entries later on
-dist: xenial
+dist: bionic
 language: c
 compiler:
   - gcc
@@ -9,7 +9,7 @@ cache:
   # There is one cache per branch and compiler version.
   # characteristics of each job are used to identify the cache:
   # - OS name (currently, linux, osx, or windows)
-  # - OS distribution (for Linux, xenial, trusty, or precise)
+  # - OS distribution (for Linux, bionic, xenial, trusty, or precise)
   # - macOS image name (e.g., xcode7.2)
   # - Names and values of visible environment variables set in .travis.yml or Settings panel
   timeout: 1200
@@ -43,7 +43,9 @@ addons:
       - libseccomp-dev
       - libspice-protocol-dev
       - libspice-server-dev
-      - libssh-dev
+# It should not install libssh-dev until the following bug is fixed:
+# https://bugs.launchpad.net/qemu/+bug/1838763
+#     - libssh-dev
       - liburcu-dev
       - libusb-1.0-0-dev
       - libvdeplug-dev
@@ -184,8 +186,7 @@ matrix:
 
 
     # Check we can build docs and tools (out of tree)
-    - name: "tools and docs (bionic)"
-      dist: bionic
+    - name: "tools and docs"
       env:
         - BUILD_DIR="out-of-tree/build/dir" SRC_DIR="../../.."
         - BASE_CONFIG="--enable-tools --enable-docs"
@@ -480,7 +481,6 @@ matrix:
 
     - name: "[s390x] GCC check-tcg"
       arch: s390x
-      dist: bionic
       addons:
         apt_packages:
           - libaio-dev
-- 
2.24.1