testsuite: skip huge test unless requested

Problem: the debian riscv64 build environment is failing on the
el capitan scaling test.

We don't have detailed test output to diagnose the failure but we
can probably assume that this is a fairly under-powered builder.

Disable the test unless TEST_LONG is set in the test environment.
Set TEST_LONG when the github workflow runs make check, so we won't
lose this coverage in github CI.

Fixes chaos#206

.github/workflows/main.yml

@@ -45,7 +45,7 @@ jobs:
     - name: make
       run: make
     - name: make check
-      run: make check
+      run: TEST_LONG=t make check
     - name: make distcheck
       run: DISTCHECK_CONFIGURE_FLAGS=--with-redfishpower make distcheck
 

t/t0039-llnl-el-capitan-cluster.t

@@ -4,6 +4,12 @@ test_description='Check LLNL El Capitan config'
 
 . `dirname $0`/sharness.sh
 
+test -n "$TEST_LONG" && test_set_prereq LONGTEST
+if ! test_have_prereq LONGTEST; then
+        skip_all='skipping large scale El Capitan test'
+        test_done
+fi
+
 ulimit -n 2048
 
 powermand=$SHARNESS_BUILD_DIRECTORY/src/powerman/powermand