Small improvements to aria recovery

I spent 4 hours on work and 12 hours of testing to try to find
the reason for aria crashing in recovery when starting a new test,
in which case the 'data directory' should be a copy of "install.db",
but aria_log.00000001 content was not correct.

The following changes are mostly done to make it a bit easier to find out
more in case of future similar crashes:

- Mark last_checkpoint_lsn volatile (safety).
- Write checkpoint message to aria_recovery.trace
- When compling with DBUG and with HAVE_DBUG_TRANSLOG_SRC,
  use checksum's for Aria log pages. We cannot have it on by default
  for DBUG servers yet as there is bugs when changing CRC between
  restarts.
- Added a message to mtr --verbose when copying the data directory.
- Removed extra linefeed in Aria recovery message (cleanup)

mysql-test/mariadb-test-run.pl

@@ -2713,6 +2713,7 @@ sub mysql_server_start($) {
         # Copy datadir from installed system db
         my $path= ($opt_parallel == 1) ? "$opt_vardir" : "$opt_vardir/..";
         my $install_db= "$path/install.db";
+        mtr_verbose("copying $install_db to $datadir");
         copytree($install_db, $datadir) if -d $install_db;
         mtr_error("Failed to copy system db to '$datadir'") unless -d $datadir;
       }