fix: use local $_ before while(<>) loops

This closes a range of bugs that can happen if a function using $_ implicitly
in a while is called in a grep {} or map {} which also uses $_

lib/perl/OVH/Bastion/os.inc

@@ -307,6 +307,7 @@ sub sys_delmemberfromgroup {
         # manually patching /etc/group... eew :(
         my $contents;
         if (open(my $fh, '<', '/etc/group')) {
+            local $_ = undef;
             while (<$fh>) {
                 if (/^\Q$group\E:/) {
                     s/([:,])\Q$user\E(?:,|$)/$1/;

lib/perl/OVH/Bastion/password.inc

@@ -124,6 +124,7 @@ sub get_hashes_list {
 
             my %metadata;
             if (open(my $metadatafd, '<', "$currentname.metadata")) {
+                local $_ = undef;
                 while (<$metadatafd>) {
                     chomp;
                     m{^([A-Z0-9_-]+)=(.+)$} or next;

lib/perl/OVH/Bastion/ssh.inc

@@ -361,6 +361,7 @@ sub get_ssh_pub_key_info {
                     $shortfp =~ s/^.{12}//;
 
                     #print "looking for shortfingerprint=$shortfp...\n";
+                    local $_ = undef;
                     while (<$fh_blacklist>) {
                         /^\Q$shortfp\E$/ or next;
                         close($fh_blacklist);