When code from MySQL 5.7.9 was merged to MariaDB 10.2.2
in commit 2e814d47
an assignment validate=true was inadvertently added to the function
dict_check_sys_tables().

This causes InnoDB to open every single .ibd file on startup, even
when no crash recovery was needed.

Simply removing the assignment would make some tests fail. We do the
best to retain almost the same level of inconsistency detection.
In the test innodb.table_flags, access to one of the tables will not
be blocked despite inconsistent flags.

dict_check_sys_tables(): Remove the problematic assignment, and skip
validation in normal startup.

dict_load_table_one(): If the .ibd file cannot be opened, mark the
table as corrupted and unreadable.

fil_node_open_file(): Validate FSP_SPACE_FLAGS with the expected
flags. If reading the tablespace fails, invalidate node->handle
instead of letting it remain stale. This bug was caught by a
fil_validate() assertion failure.

fsp_flags_try_adjust(): If the tablespace file is invalid, do nothing.