better logging for substeps, and use undef for ccList in email r=preed

tools/release/Bootstrap/Step/Tag.pm

@@ -85,7 +85,7 @@ sub Execute {
     while ($currentStep < $numSteps) {
         my $stepName = $subSteps[$currentStep];
         eval {
-            $this->Log(msg => 'Tag running substep' . $stepName);
+            $this->Log(msg => 'Tag running substep ' . $stepName);
             my $step = "Bootstrap::Step::Tag::$stepName"->new();
             $step->Execute();
         };
@@ -113,7 +113,7 @@ sub Verify {
     while ($currentStep < $numSteps) {
         my $stepName = $subSteps[$currentStep];
         eval {
-            $this->Log(msg => 'Tag running substep' . $stepName);
+            $this->Log(msg => 'Tag running substep ' . $stepName);
             my $step = "Bootstrap::Step::Tag::$stepName"->new();
             $step->Verify();
         };

tools/release/MozBuild/Util.pm

@@ -311,7 +311,7 @@ sub Email {
 
     my $from = $args{'from'};
     my $to = $args{'to'};
-    my $ccList = $args{'cc'} ? $args{'cc'} : '';
+    my $ccList = $args{'cc'} ? $args{'cc'} : undef;
     my $subject = $args{'subject'};
     my $message = $args{'message'};
     my $sendmail = $args{'sendmail'};