drone: Update to Drone v0.5 yaml format

.drone.yml

-image: riot/riotbuild:latest
-
-env:
-    - NPROC_MAX=8
-
-script:
-    - git config --global user.email "drone@example.com"
-    - git config --global user.name "Drone CI"
-    - git remote add riot https://github.com/RIOT-OS/RIOT.git
-    - git fetch riot master
-    - git log -1 --pretty=format:%H riot/master
-    - git branch -f master riot/master
-    - pwd
-    - set
-    - git status
-    - git branch
-    - git remote -v
-    - git branch -avv
-    - ./dist/tools/drone-scripts/build_and_test.sh riot/master
+pipeline:
+    run_tests:
+        image: riot/riotbuild:latest
+        environment:
+            - CLICOLOR_FORCE=1
+            - NPROC_MAX=4
+        commands:
+            - pwd
+            - printenv
+            - git status
+            - git remote -v
+            - ./dist/tools/travis-scripts/build_and_test.sh
+matrix:
+    BUILDTEST_MCU_GROUP:
+        - static-tests
+        - cortex_m4_3
+        - cortex_m4_2
+        - cortex_m4_1
+        - cortex_m0_2
+        - cortex_m0_1
+        - x86
+        - cortex_m3_2
+        - cortex_m3_1
+        - avr8
+        - msp430
+        - arm7
+        - host