Use .go-version to specify the Go version for all CI builds (elastic#…

…4303)

Having a simple file that requires no parsing to retrieve the Go version
provides us a standard portable way to know what Go version to use for builds.
It's basically the least common denominator for builds accross CI systems
(Jenkins, AppVeyor, Travis) and operating systems.

Also changed AppVeyor to invalidate the cached Go version only when the
.go-version file changes instead of when the .appveyor.yml changes.

.appveyor.yml

@@ -7,7 +7,6 @@ os: Windows Server 2012 R2
 # Environment variables
 environment:
   GOPATH: c:\gopath
-  GVM_GO_VERSION: 1.8.1
   GVM_DL: https://github.com/andrewkroh/gvm/releases/download/v0.0.1/gvm-windows-amd64.exe
   PYWIN_DL: https://beats-files.s3.amazonaws.com/deps/pywin32-220.win32-py2.7.exe
   matrix:
@@ -25,7 +24,7 @@ clone_folder: c:\gopath\src\github.com\elastic\beats
 cache:
 - C:\ProgramData\chocolatey\bin -> .appveyor.yml
 - C:\ProgramData\chocolatey\lib -> .appveyor.yml
-- C:\Users\appveyor\.gvm -> .appveyor.yml
+- C:\Users\appveyor\.gvm -> .go-version
 - C:\Windows\System32\gvm.exe -> .appveyor.yml
 - C:\tools\mingw64 -> .appveyor.yml
 - C:\pywin_inst.exe -> .appveyor.yml
@@ -36,7 +35,7 @@ install:
       if(!(Test-Path "C:\Windows\System32\gvm.exe")) {
         wget "$env:GVM_DL" -Outfile C:\Windows\System32\gvm.exe
       }
-  - ps: gvm --format=powershell "$env:GVM_GO_VERSION" | Invoke-Expression
+  - ps: gvm --format=powershell $(Get-Content .go-version) | Invoke-Expression
   # AppVeyor installed mingw is 32-bit only so install 64-bit version.
   - ps: >-
       if(!(Test-Path "C:\tools\mingw64\bin\gcc.exe")) {

.go-version

@@ -0,0 +1 @@
+1.8.1

.travis.yml

@@ -12,73 +12,73 @@ env:
   global:
     # Cross-compile for amd64 only to speed up testing.
     - GOX_FLAGS="-arch amd64"
-    - DOCKER_COMPOSE_VERSION: 1.11.1
-    - &go_version 1.8.1
+    - DOCKER_COMPOSE_VERSION=1.11.1
+    - GO_VERSION="$(cat .go-version)"
 
 matrix:
   include:
     # General checks
     - os: linux
       env: TARGETS="check"
-      go: *go_version
+      go: $GO_VERSION
 
     # Filebeat
     - os: linux
       env: TARGETS="-C filebeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
     - os: osx
       env: TARGETS="TEST_ENVIRONMENT=0 -C filebeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
 
     # Heartbeat
     - os: linux
       env: TARGETS="-C heartbeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
     - os: osx
       env: TARGETS="TEST_ENVIRONMENT=0 -C heartbeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
 
     # Libbeat
     - os: linux
       env: TARGETS="-C libbeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
     - os: linux
       env: TARGETS="-C libbeat crosscompile"
-      go: *go_version
+      go: $GO_VERSION
 
     # Metricbeat
     - os: linux
       env: TARGETS="-C metricbeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
     - os: osx
       env: TARGETS="TEST_ENVIRONMENT=0 -C metricbeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
     - os: linux
       env: TARGETS="-C metricbeat crosscompile"
-      go: *go_version
+      go: $GO_VERSION
 
     # Packetbeat
     - os: linux
       env: TARGETS="-C packetbeat testsuite"
-      go: *go_version
+      go: $GO_VERSION
 
     # Winlogbeat
     - os: linux
       env: TARGETS="-C winlogbeat crosscompile"
-      go: *go_version
+      go: $GO_VERSION
 
     # Dashboards
     - os: linux
       env: TARGETS="-C dev-tools/cmd/import_dashboards"
-      go: *go_version
+      go: $GO_VERSION
 
     # Generators
     - os: linux
       env: TARGETS="-C generator/metricbeat test"
-      go: *go_version
+      go: $GO_VERSION
     - os: linux
       env: TARGETS="-C generator/beat test"
-      go: *go_version
+      go: $GO_VERSION
 
 addons:
   apt:

dev-tools/common.bash

@@ -27,7 +27,7 @@ err()
 # Read the project's Go version and return it in the GO_VERSION variable.
 # On failure it will exit.
 get_go_version() {
-  GO_VERSION=$(awk '/^:go-version:/{print $NF}' "${_sdir}/../libbeat/docs/version.asciidoc")
+  GO_VERSION=$(cat "${_sdir}/../.go-version")
   if [ -z "$GO_VERSION" ]; then
     err "Failed to detect the project's Go version"
     exit 1