osbuild-run: make update-ca-trust optional

This is a RHism, that is not available on Debian-based systems.
Do not make it a hard reqirement, as pipelines may be able to
function just fine without it.

In a follow-up commit we will also check for the Debian-based
equivalent.

Signed-off-by: Tom Gundersen <teg@jklm.no>

osbuild-run

@@ -1,5 +1,6 @@
 #!/usr/bin/python3
 
+import shutil
 import os
 import subprocess
 import sys
@@ -20,6 +21,9 @@ def sysusers():
 
 
 def update_ca_trust():
+    if not shutil.which("update-ca-trust"):
+        return
+
     # generate /etc/pki/tls/certs/ca-bundle.crt
     os.makedirs("/etc/pki/ca-trust/extracted/pem")
     os.makedirs("/etc/pki/tls/certs")