use multicore for BiocParallel

reason is to
(1) have real environment that we're exporting to
(2) previous test's register_dopar() is not unregistered, hence cmq
tries to use multicore that requires this option set

tests/testthat/test-8-foreach.r

@@ -89,8 +89,14 @@ test_that("external worker", {
 })
 
 test_that("foreach works via BiocParallel", {
+    skip_on_os("windows")
     skip_if_not_installed("BiocParallel")
 
+    old_sched = getOption("clustermq.scheduler")
+    on.exit(options(clustermq.scheduler = old_sched))
+    options(clustermq.scheduler = "multicore")
+
+    register_dopar_cmq(n_jobs=1)
     BiocParallel::register(BiocParallel::DoparParam())
     res = BiocParallel::bplapply(1:3, sqrt)
     cmp = foreach(i=1:3) %do% sqrt(i)