Support PBS executor type

Closes #46 (closed)

build/containers/pbs-tester/Dockerfile

+FROM registry.gitlab.com/ecp-ci/jacamar-ci/centos7-builder:latest
+
+# OpenPBS test container
+# https://github.com/openpbs/openpbs/blob/master/INSTALL
+
+RUN   yum install -y \
+        # PBS build reqs
+        autoconf \
+        automake \
+        expat-devel \
+        gcc \
+        gcc-c++ \
+        hwloc-devel \
+        libedit-devel \
+        libical-devel \
+        libtool \
+        libX11-devel \
+        libXext \
+        libXft \
+        libXt-devel \
+        make \
+        ncurses-devel \
+        openssl-devel \
+        perl \
+        postgresql-contrib \
+        postgresql-devel \
+        python3-devel \
+        rpm-build \
+        swig \
+        tcl-devel \
+        tk-devel \
+        # PBS run reqs
+        expat \
+        libical \
+        libedit \
+        postgresql-contrib \
+        postgresql-server \
+        python3 \
+        sendmail \
+        sudo \
+        tcl \
+        tk \
+        # Misc tools
+        vim \
+    && yum clean all \
+    && useradd -ms /bin/bash pbsadmin \
+    && useradd -ms /bin/bash pbsuser \
+    && echo "pbsadmin ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers \
+    && mkdir /pbs \
+    && chmod 777 /pbs
+
+ARG PBS_VER="20.0.1"
+
+USER pbsadmin
+WORKDIR /pbs
+RUN wget https://github.com/openpbs/openpbs/archive/refs/tags/v${PBS_VER}.tar.gz \
+    && tar -xvf v${PBS_VER}.tar.gz \
+    && cd openpbs-${PBS_VER} \
+    && ./autogen.sh \
+    && ./configure --prefix=/opt/pbs \
+    && make \
+    && sudo make install \
+    && cd / \
+    && sudo rm -rf /pbs
+
+USER root
+COPY entry.bash /entry.bash
+WORKDIR /
+RUN /opt/pbs/libexec/pbs_postinstall \
+    && sed -i 's/PBS_START_MOM\=0/PBS_START_MOM\=1/' /etc/pbs.conf \
+    && chmod 4755 /opt/pbs/sbin/pbs_iff /opt/pbs/sbin/pbs_rcp \
+    && echo "source /etc/profile.d/pbs.sh" >> /etc/profile \
+    && chmod 755 /entry.bash
+
+# Note, the container must be ran with "buildkitsandbox" hostname in order to function.
+ENTRYPOINT ["/entry.bash"]