Parallelize Slurm build

Dockerfile

@@ -16,7 +16,7 @@ RUN dnf download --source slurm && \
     cd /root/rpmbuild/SPECS && \
     sed -i "s/--disable-multiple-slurmd/--enable-multiple-slurmd/" slurm.spec && \
     dnf builddep -y slurm.spec && \
-    rpmbuild -bb slurm.spec && \
+    RPM_BUILD_NCPUS=$(nproc) rpmbuild -bb slurm.spec && \
     cd /root/rpmbuild/RPMS/x86_64 && \
     dnf install -y slurm{,-libs,-devel,-perlapi,-slurm{ctld,d,dbd}}-$(ls slurm* | head -n 1 | cut -d - -f 2-) && \
     cd / && \