Added recipe for the Singularity container platform.

Singularity is a container platform built on the principle of mobility
of compute.  It is designed to be used on HPC clusters and, unlike
Docker, it does not require root access to mount an image. In addition,
it can use Docker images out-of-the-box and it can pull them from the
Docker Hub. For more information, see singularity.lbl.gov

This recipe enables building the Singularity container platform.
Additionally, it creates a symlink from /usr/bin/python3 to
/usr/bin/python, as well as a symlink to where python3 expects
CA certificates to be.

I have tested it on a Raspberry Pi 3: I successfully built and run
arm32v7 images from Docker Hub. Make sure you have the right image for
your CPU architecture: it defaults to amd64.

Signed-off-by: Alexandru Tiniuc <tiniuc.alexandru at gmail dot com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>

recipes-containers/singularity/singularity_git.bb

@@ -0,0 +1,35 @@
+# Skip QA check for library symbolic links (core issue is a packaging problem within 
+# Singularity build / config: read up on the dev-so test for more info)
+INSANE_SKIP_${PN} += "dev-so"
+
+RDEPENDS_${PN} += "glibc python3 ca-certificates openssl"
+# Singularity expects to find python3 under the name python, therefore both
+# cannot be installed at the same time.
+RCONFLICTS_${PN} = "python"
+
+LICENSE = "BSD"
+LIC_FILES_CHKSUM = "file://COPYRIGHT.md;md5=be78c34e483dd7d8439358b1e024b294 \
+                    file://LICENSE-LBNL.md;md5=45a007b527e1a9507aa7fa869f8d7ede \
+                    file://LICENSE.md;md5=df4326b473db6424033f1d98a5645e30 \
+                    file://debian/copyright;md5=ed267cf386d9b75ab1f27f407e935b10"
+
+SRC_URI = "git://github.com/singularityware/singularity.git;protocol=https"
+PV = "2.3.1+git${SRCPV}"
+SRCREV = "e214d4ebf0a1274b1c63b095fd55ae61c7e92947"
+
+S = "${WORKDIR}/git"
+
+inherit pythonnative autotools-brokensep
+EXTRA_OECONF = "--prefix=/usr/local"
+
+pkg_postinst_${PN}() {
+    # Singularity requires "python" to resolve to "python3" within the commandline.
+    # This creates a symbolic link from python3 to python. A side-effect of this is
+    # that scripts which expect Python 2 may fail to run correctly.
+    ln -sr $D${bindir}/python3 $D${bindir}/python 
+
+    # python3 expects CA certificates to be installed in a different place to where
+    # they are actually installed. These lines link the two locations.
+    rm -r $D${libdir}/ssl-1.1/certs
+    ln -sr $D${sysconfdir}/ssl/certs $D${libdir}/ssl-1.1 
+}