[monitoring-plugin-perl] Add missing `label` key to named Getopts args

[Sven Nierlein]

    Module: monitoring-plugin-perl
    Branch: master
    Commit: 4aa2aee51b54cb8988d87a01d1a3b9a0d90bb8bf
    Author: Tom Ryder <tom at sanctum.geek.nz>
 Committer: Sven Nierlein <sven at nierlein.de>
      Date: Wed Oct 25 10:03:18 2017 +1300
       URL: https://www.monitoring-plugins.org/repositories/monitoring-plugin-perl/commit/?id=4aa2aee

Add missing `label` key to named Getopts args

If the `label` key is given as a named argument for argument
specification, if it turns out to be the first element returned in the
argument list subject to hash randomization, then this test for named
arguments fails due to the omission of the label from this alternating
group in the pattern.

When this happens, the code for an unnamed list of items was run
instead, leading to a very confusing area happening randomly:

    8 parameters were passed to Monitoring::Plugin::Getopt::arg but 2 - 5 were expected
     at PERL/lib/perl5/Monitoring/Plugin/Getopt.pm line 397.
            Monitoring::Plugin::Getopt::arg(undef, "label", "HOSTNAME", "required", 1, "help", "Hostname of device to check", "spec", ...) called at PERL/lib/perl5/Monitoring/Plugin.pm line 161
            Monitoring::Plugin::add_arg(Monitoring::Plugin=HASH(0x1f90fd8), "label", "HOSTNAME", "required", 1, "help", "Hostname of device to check", "spec", ...) called at libexec/check_example line 144

If you specified all five keys for your argument, then this happens
(roughly) one-fifth of the time.

---

 lib/Monitoring/Plugin/Getopt.pm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Monitoring/Plugin/Getopt.pm b/lib/Monitoring/Plugin/Getopt.pm
index 9452058..262e3c8 100644
--- a/lib/Monitoring/Plugin/Getopt.pm
+++ b/lib/Monitoring/Plugin/Getopt.pm
@@ -383,7 +383,7 @@ sub arg
   my %args;
 
   # Named args
-  if ($_[0] =~ m/^(spec|help|required|default)$/ && scalar(@_) % 2 == 0) {
+  if ($_[0] =~ m/^(spec|help|required|default|label)$/ && scalar(@_) % 2 == 0) {
     %args = validate( @_, {
       spec => 1,
       help => 1,