MT#56004 functions: Add a fallback value for NGCPCFG_PID

This variable is assumed to be set and exported by ngcpcfg when it
starts running. But we have code (in the ngcp-upgrade steps), which
calls the restore-permissions helper directly w/o going through ngcpcfg,
and which then breaks when the variable is not yet set.

Add a fallback value so that we do not fail anymore. But we should
eventually expose this functionality as an actual command as part of
the public ngcpcfg CLI.

Change-Id: Ibda18faaff8a26a04240e6ed7a46ee7650b82954

functions/logs

@@ -24,7 +24,10 @@ console_output() {
 
 ## logging functions {{{
 log_only() {
-  logger -t ngcpcfg --id="${NGCPCFG_PID}" -- "$*"
+  # XXX: The NGCPCFG_PID variable should be set by ngcpcfg, but we currently
+  # have code that executes helpers directly, where we should have exposed
+  # those helpers as new commands. For now we fallback to the current PID.
+  logger -t ngcpcfg --id="${NGCPCFG_PID:-$$}" -- "$*"
 }
 
 log_info() {