build: allow to test RPM / Deb packages locally

Provided the script to build a RPM / Deb package, install it inside a
docker container based on an appropriate image and verify that the main
class of the extension (Tarantool) is available from the PHP
interpreter.

The script builds a package just like it is performed in CI: using
packpack. It should be available in PATH directories.

Only RPM packages are here now, but the following commits will enable
Deb packages too.

Part of #117

test.pkg.all.sh

@@ -0,0 +1,37 @@
+#!/bin/sh
+
+set -exu  # Strict shell (w/o -o pipefail)
+
+distros="
+    el:8
+    fedora:25
+    fedora:26
+    fedora:27
+    fedora:28
+    fedora:29
+    fedora:30
+    fedora:31
+"
+
+if ! type packpack; then
+    echo "Unable to find packpack"
+    exit 1
+fi
+
+for distro in $distros; do
+    export OS="${distro%%:*}"
+    export DIST="${distro#*:}"
+    if [ "${OS}" = "el" ]; then
+        export OS=centos
+    fi
+
+    rm -rf build
+    packpack
+
+    docker run \
+        --volume "$(realpath .):/tarantool-php" \
+        --workdir /tarantool-php                \
+        --rm                                    \
+        "${OS}:${DIST}"                         \
+        ./test.pkg.sh
+done