Enable Concourse caching of ccache

Shiny new feature in Concourse 3.3.0
(https://concourse.ci/running-tasks.html#caches)

[ci skip]

concourse/build_and_test.py

@@ -48,7 +48,16 @@ def make():
         "-j" + str(num_cpus()),
         "-l" + str(2 * num_cpus()),
         ],
-        cwd="build")
+        cwd="build",
+        env=ccache_env()
+        )
+
+
+def ccache_env():
+    env = os.environ.copy()
+    env['CCACHE_DIR'] = os.getcwd() + '/.ccache'
+    return env
+
 
 def run_tests():
     return subprocess.call(["ctest",

concourse/build_and_test_centos5_debug.yml

@@ -9,6 +9,10 @@ inputs:
   - name: orca_src
 outputs:
   - name: build_and_test_debug
+
+caches:
+  - path: .ccache
+
 run:
   path: orca_src/concourse/build_and_test.py
   args:

concourse/build_and_test_centos5_release.yml

@@ -7,6 +7,10 @@ image_resource:
 inputs:
   - name: bin_xerces_centos5
   - name: orca_src
+
+caches:
+  - path: .ccache
+
 outputs:
   - name: build_and_test_release
 run: