job: Rename BlockJobType into JobType

QAPI types aren't externally visible, so we can rename them without
causing problems. Before we add a job type to Job, rename the enum
so it can be used for more than just block jobs.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>

block/commit.c

@@ -218,7 +218,7 @@ static const BlockJobDriver commit_job_driver = {
     .job_driver = {
         .instance_size = sizeof(CommitBlockJob),
     },
-    .job_type      = BLOCK_JOB_TYPE_COMMIT,
+    .job_type      = JOB_TYPE_COMMIT,
     .start         = commit_run,
 };