Bug#26989949: make main.basedir work with renamed binary

Problem: main.basedir did not work with renamed binaries (mysqld-debug)
Solution: Fix perl-regexps so that they do not hard code the name of the
binary.

Change-Id: I7c03864e207b70fed313a432ef5f4718200b8522

Author: Dyre Tjeldvoll

mysql-test/t/basedir.test

@@ -92,7 +92,9 @@ EOF
   $ENV{'PATH'}="$bindir:$ENV{'PATH'}";
 
   my $init_file_args= $ENV{'INIT_FILE_ARGS'};
-  (system("mysqld $init_file_args") == 0) ||
+  my $binary= $ENV{'MYSQLD'};
+  $binary =~ s|$bdir/||;
+  (system("$binary $init_file_args") == 0) ||
     die "system failed on 'mysqld $init_file_args': $!";
 
   my $mysqld_log= $ENV{'MYSQLD_LOG'};