Fallback to podman automatically if docker is not installed

Signed-off-by: Yann Dirson <[email protected]>

build.sh

@@ -8,7 +8,22 @@ if [ -z "$1" ]; then
     exit
 fi
 
-RUNNER="${XCPNG_OCI_RUNNER:-docker}"
+RUNNER=""
+if [ -n "$XCPNG_OCI_RUNNER" ]; then
+    RUNNER="$XCPNG_OCI_RUNNER"
+else
+    SUPPORTED_RUNNERS="docker podman"
+    for COMMAND in $SUPPORTED_RUNNERS; do
+        if command -v $COMMAND >/dev/null; then
+            RUNNER="$COMMAND"
+            break
+        fi
+    done
+    if [ -z "$RUNNER" ]; then
+        echo >&2 "cannot find a supported runner: $SUPPORTED_RUNNERS"
+        exit 1
+    fi
+fi
 
 cd $(dirname "$0")
 

run.py

@@ -20,7 +20,15 @@
 DEFAULT_BRANCH = '8.3'
 DEFAULT_ULIMIT_NOFILE = 1024
 
-RUNNER = os.getenv("XCPNG_OCI_RUNNER", "docker")
+RUNNER = os.getenv("XCPNG_OCI_RUNNER")
+if RUNNER is None:
+    SUPPORTED_RUNNERS = "docker podman"
+    for command in SUPPORTED_RUNNERS.split():
+        if shutil.which(command):
+            RUNNER = command
+            break
+    else:
+        raise Exception(f"cannot find a supported runner: {SUPPORTED_RUNNERS}")
 
 def make_mount_dir():
     """ Make a randomly-named directory under SRPMS_MOUNT_ROOT. """