various: do not include file names directly in error messages

git grep -l 'Failed to open /'|xargs sed -r -i 's|"Failed to open (/[^ ]+): %m"|"Failed to open %s: %m", "\1"|g'
git grep -l $'Failed to open \'/'|xargs sed -r -i $'s|"Failed to open \'(/[^ ]+)\': %m"|"Failed to open %s: %m", "\\1"|g'
git grep -l "Failed to open /"|xargs sed -r -i $'s|"Failed to open (/[^ ]+), ignoring: %m"|"Failed to open %s, ignoring: %m", "\\1"|g'
+ some manual fixups.

src/resolve/resolved-etc-hosts.c

@@ -365,7 +365,7 @@ static int manager_etc_hosts_read(Manager *m) {
         f = fopen("/etc/hosts", "re");
         if (!f) {
                 if (errno != ENOENT)
-                        return log_error_errno(errno, "Failed to open /etc/hosts: %m");
+                        return log_error_errno(errno, "Failed to open %s: %m", "/etc/hosts");
 
                 manager_etc_hosts_flush(m);
                 return 0;

src/resolve/resolved-resolv-conf.c

@@ -106,7 +106,7 @@ int manager_read_resolv_conf(Manager *m) {
                 if (errno == ENOENT)
                         return 0;
 
-                r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
+                r = log_warning_errno(errno, "Failed to open %s: %m", "/etc/resolv.conf");
                 goto clear;
         }