Rename gctl.t to gctl_test.t and test.c to gctl_test_helper.c

This is being done to reduce ambiguity and to make the tests more portable
in the future to other locations in the source tree.

MFC after:	5 weeks
Sponsored by:	Dell EMC Isilon

tools/regression/geom_gpt/gctl_test.t

@@ -132,7 +132,7 @@ if (exists $ENV{'TEST_VERBOSE'}) {
 }
 
 # Compile the driver...
-my $st = system("cc -o $cmd -g $srcdir/test.c -lgeom");
+my $st = system("cc -o $cmd -g $srcdir/gctl_test_helper.c -lgeom");
 if ($st != 0) {
     print "1..0 # SKIP error compiling test.c\n";
     exit 0;