runners: add rhel7 runner

Create a runner for RHEL7. The one thing to note is that RHEL 7
makes use of ld.so.confd snippets and one important for us is
to include `/usr/lib64/iscsi` needed by qemu-img. Otherwise this
is a fairly simple and straight forward runner.

runners/org.osbuild.rhel7

@@ -0,0 +1,35 @@
+#!/usr/bin/python3
+
+import os
+import subprocess
+import sys
+
+import osbuild.api
+
+
+def ldconfig():
+    # ld.so.conf must exist, or `ldconfig` throws a warning
+    with open("/etc/ld.so.conf", "w", ) as f:
+        # qemu-img needs `libiscsi`, which is located in /usr/lib64/iscsi
+        f.write("/usr/lib64/iscsi\n")
+        f.flush()
+    subprocess.run(["ldconfig"], check=True)
+
+
+def nsswitch():
+    # the default behavior is fine, but using nss-resolve does not
+    # necessarily work in a non-booted container, so make sure that
+    # is not configured.
+    try:
+        os.remove("/etc/nsswitch.conf")
+    except FileNotFoundError:
+        pass
+
+
+if __name__ == "__main__":
+    with osbuild.api.exception_handler():
+        ldconfig()
+        nsswitch()
+
+        r = subprocess.run(sys.argv[1:], check=False)
+        sys.exit(r.returncode)