INSTALL/UNINSTALL WITH CTRL+C

Description: If we try to cancel install/uninstall operation
using ctrl+c then there multiple component entries exists in
mysql.component table for same component

Analysis:
1) For Install component in mysql_persistent_dynamic_loader_imp::load()
   the thd->killed flag is checked only at open_component_table()
2) For Uninstall component in mysql_persistent_dynamic_loader_imp::unload()
   the thd->killed flag is checked in two places open_component_table() and h
At #1, when kill query is recieved before open_component_table() fails
with below error
  "The mysql.component table is missing or has an incorrect definition."
And after open_component_table() thd->killed is not checked so, no roll
back of tnx happens at all.
At #2, when kill query is recieved before open_component_table() same,
behaviour as #1.
And when kill query is recieved just before ha_index_read_idx_map()
(and say, after first iteration),
then ha_index_read_idx_map() fails with error returned from the SE.
And the roll back of transactions happens.
But here, by then the dynamic_loader::unload has been done
(Which is a undone operation). And also
mysql_persistent_dynamic_loader_imp::component_id_by_urn has been updated.
This mysql_persistent_dynamic_loader_imp::component_id_by_urn variable
is used to controll the INSTALL/UNINSTALL urns from mysql.component table.
Since the dynamic_loader::unload has been done and those urns also
removed from mysql_persistent_dynamic_loader_imp::component_id_by_urn
(but the not removed from mysql.component table because of
 ha_index_read_idx_map() failure), the next INSTALL COMPONENT stmt again
adds the urns to the mysql.component table.
This leads to residues in mysql.component table.

Fix:
For #1, It was noticed that If open_component_table() fails because
of kill query, then the roll back of dynamic_loader::load is not done,
this is because of mysql_dynamic_loader_imp::load() is called before
open_component_table() and guard for mysql_dynamic_loader_imp::load()
is registered after the open_component_table().
Hence fixed that, by arranging calls open_component_table(),
mysql_dynamic_loader_imp::load() and guard for
mysql_dynamic_loader_imp::load.
And by chance if there is a failure form ha_write_row(), in that case,
mysql_persistent_dynamic_loader_imp::component_id_by_urn variable has
to be reset. So, did that.
For #2, The mysql_dynamic_loader_imp::unload operation has been moved
after ha_index_read_idx_map()/ha_index_read_idx_map() calls.
Along with this mysql_persistent_dynamic_loader_imp::component_id_by_urn
is restored in error cases of
ha_index_read_idx_map()/ha_index_read_idx_map().
By moving mysql_dynamic_loader_imp::unload() to end, it helps in
not having to undo the unload operation.