Bug 1350390: make fields that were unnecesarily optional, required; r=Callek

Docker-worker's `command` field is actually not required, as it will run a
docker image's default command when command is not specified.

MozReview-Commit-ID: I3vBHeixlxW

taskcluster/taskgraph/transforms/task.py

@@ -201,11 +201,12 @@ task_description_schema = Schema({
         # environment variables
         Required('env', default={}): {basestring: taskref_or_string},
 
-        # the command to run
-        'command': [taskref_or_string],
+        # the command to run; if not given, docker-worker will default to the
+        # command in the docker image
+        Optional('command'): [taskref_or_string],
 
         # the maximum time to run, in seconds
-        'max-run-time': int,
+        Required('max-run-time'): int,
 
         # the exit status code that indicates the task should be retried
         Optional('retry-exit-status'): int,
@@ -214,7 +215,7 @@ task_description_schema = Schema({
         Required('implementation'): 'generic-worker',
 
         # command is a list of commands to run, sequentially
-        'command': [taskref_or_string],
+        Required('command'): [taskref_or_string],
 
         # artifacts to extract from the task image after completion; note that artifacts
         # for the generic worker cannot have names
@@ -239,7 +240,7 @@ task_description_schema = Schema({
         Required('env', default={}): {basestring: taskref_or_string},
 
         # the maximum time to run, in seconds
-        'max-run-time': int,
+        Required('max-run-time'): int,
 
         # os user groups for test task workers
         Optional('os-groups', default=[]): [basestring],
@@ -248,14 +249,14 @@ task_description_schema = Schema({
 
         # see
         # https://github.com/mozilla/buildbot-bridge/blob/master/bbb/schemas/payload.yml
-        'buildername': basestring,
-        'sourcestamp': {
+        Required('buildername'): basestring,
+        Required('sourcestamp'): {
             'branch': basestring,
             Optional('revision'): basestring,
             Optional('repository'): basestring,
             Optional('project'): basestring,
         },
-        'properties': {
+        Required('properties'): {
             'product': basestring,
             Extra: basestring,  # additional properties are allowed
         },