mxmount: Allow "=" in variable values

Currently mxmounts fails when we set

    DEFAULT_EXPORT_OPTIONS=@amd(sync,rw,no_root_squash,no_subtree_check,insecure_locks,sec=sys:mariux)

with

    Unmatched ( in regex; marked by <-- HERE in m/DEFAULT_EXPORT_OPTIONS=@amd( <-- HERE sync,rw,no_root_squash,no_subtree_check,insecure_locks,sec/ at /usr/bin/mxmount line 212.

Use non-greedy pattern for ""VAR=value".

mxmount/mxmount

@@ -221,7 +221,7 @@ sub parse_variables {
    my ($key, $value);
 
    foreach(@lines) {
-        if(($key, $value) = /^(\S+)=\s*(.*)$/) {
+        if(($key, $value) = /^(\S+?)=\s*(.*)$/) {
             $V{$key} = $value;
         } else {
             push @invalid,expand_variables($_);