Allow InnoDB I_S plugins to be installed when InnoDB storage engine is
not installed but show empty tables when SELECTing from them in this
case. Set srv_was_started to FALSE at the end of
innobase_shutdown_for_mysql() so the I_S plugins can detect if InnoDB is
uninstalled.
 
This is needed to workaround the MySQL
Bug#36399 Double free bug when INFORMATION_SCHEMA plugin init function fails
and is more flexible as it allows I_S plugins to be installed before the
InnoDB plugin and detects if the latter is uninstalled after this.

Approved by:	Heikki