Add Vagrant build environment (elastic/elasticsearch#38)

This adds a vagrant configuration under /vagrant. This allows the user to provision a virtual machine with the entire build environment needed for compiling the C++ portion of the code (as well as the Java side, but that can be done easily outside of vagrant).

Original commit: elastic/x-pack-elasticsearch@12754bd80e

vagrant/.gitignore

@@ -0,0 +1 @@
+.vagrant

vagrant/README.md

@@ -0,0 +1,83 @@
+## Vagrant build environment
+
+This provides a vagrant box for building the C++ side of Prelert (and the Java side,
+although that is easily accomplished outside vagrant).
+
+Provisioning the box will take a fair amount of time, since it needs to download
+and compile a number of dependencies.
+
+A pre-provisioned box can be downloaded from: TODO
+
+### Details
+- Ubuntu Trusty64 (14.04.5 LTS)
+- 25% of host's memory
+- 100% host's cores
+- Maps prelert source repository to `/home/vagrant/prelert/src`
+  - Directory is shared with the host, so you can point your IDE to the prelert repo
+    and build inside vagrant
+- Maps prelert build directory to `/home/vagrant/prelert/build`
+- Changes into `/home/vagrant/prelert/src` on login
+
+### Usage
+
+```bash
+$ cd prelert-legacy
+$ cd vagrant
+$ vagrant up
+  # ...
+  # wait while vagrant provisions
+  # ...
+$ vagrant ssh
+
+Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 3.13.0-96-generic x86_64)
+
+ * Documentation:  https://help.ubuntu.com/
+
+  System information as of Tue Oct  4 16:06:31 UTC 2016
+
+  System load:  0.0                Processes:           196
+  Usage of /:   12.0% of 39.34GB   Users logged in:     0
+  Memory usage: 2%                 IP address for eth0: 10.0.2.15
+  Swap usage:   0%
+
+  Graph this data and manage this system at:
+    https://landscape.canonical.com/
+
+  Get cloud support with Ubuntu Advantage Cloud Guest:
+    http://www.ubuntu.com/business/services/cloud
+
+New release '16.04.1 LTS' available.
+Run 'do-release-upgrade' to upgrade to it.
+
+
+Last login: Tue Oct  4 16:06:32 2016 from 10.0.2.2
+vagrant@vagrant-ubuntu-trusty-64:~/prelert/src$
+```
+
+Once you've logged into the box, you'll be in the prelert source directory. You
+can build immediately via:
+
+```bash
+vagrant@vagrant-ubuntu-trusty-64:~/prelert/src$ gradle cppmake
+  # ...
+  # much building
+  # ...
+```
+
+### Suspending your box
+Once you've provisioned a box, you can use `vagrant suspend` to "sleep" the box.
+This has the advantage of rebooting quickly when you `vagrant up`, and returns you
+to exactly what you were doing.  On the downside, it eats more disk space since it
+needs to sleep the entire image.
+
+You can alternatively use `vagrant halt`, which gracefully powers down the machine.
+Rebooting via `vagrant up` takes longer since you are rebooting the entire OS,
+but it saves more disk space.
+
+### Fixing a broken box
+If you accidentally kill the provisioning process before it completes, you can
+attempt to reprovision it with `vagrant reload --provision`.  That will run
+the provisioners that did not complete previously.
+
+If your box is still horribly broken, you can destroy it with `vagrant destroy`
+and try again with `vagrant up`  

vagrant/Vagrantfile

@@ -0,0 +1,29 @@
+Vagrant.configure(2) do |config|
+  config.vm.box = "ubuntu/trusty64"
+  config.vm.provider "virtualbox" do |v|
+    host = RbConfig::CONFIG['host_os']
+
+    # Give VM 1/4 system memory
+    linux = RUBY_PLATFORM =~ /linux/
+    osx = RUBY_PLATFORM =~ /darwin/
+    windows = (/cygwin|mswin|mingw|bccwin|wince|emx/ =~ RUBY_PLATFORM) != nil
+    if osx
+      cpus = `sysctl -n hw.ncpu`.to_i
+      mem = `sysctl -n hw.memsize`.to_i / 1024 / 1024
+    end
+    if linux
+      cpus = `nproc`.to_i
+      mem = `sed -n -e '/^MemTotal/s/^[^0-9]*//p' /proc/meminfo`.to_i / 1024
+    end
+    if windows
+      cpus = `wmic computersystem get numberofprocessors`.split("\n")[2].to_i
+      mem = `wmic OS get TotalVisibleMemorySize`.split("\n")[2].to_i / 1024
+    end
+
+    mem = mem / 4
+    v.customize ["modifyvm", :id, "--memory", mem]
+    v.customize ["modifyvm", :id, "--cpus",  cpus]
+  end
+  config.vm.provision :shell, path: "provision.sh"
+  config.vm.synced_folder "../", "/home/vagrant/prelert/src", mount_options: ["dmode=777,fmode=777"]
+end