[WIP] Install `curl` command by default.
Install `curl` by default.

```
diff --git a/site-cookbooks/base/recipes/packages.rb b/site-cookbooks/base/recipes/packages.rb
index 3a5e8b2..e57e763 100644
--- a/site-cookbooks/base/recipes/packages.rb
+++ b/site-cookbooks/base/recipes/packages.rb
@@ -64,3 +64,8 @@ end
 package "dstat" do
   action :install
 end
+
+# curl installation:
+package "curl" do
+  action :install
+end
```
Add test for installing `curl`.

```
diff --git a/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb b/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb
index 1b8ce0f..e5ed748 100644
--- a/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb
+++ b/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb
@@ -37,3 +37,7 @@ end
 describe package('dstat') do
   it { should be_installed }
 end
+
+describe package('curl') do
+  it { should be_installed }
+end
```
Merge pull request #162 from kazu634/curl-installation

Install `curl` command by default.