KEYRING_FILE_DATA OPTION

DESCRIPTION
===========
Initializing datadir with the keyring_file_data option
fails with the following error:

[ERROR] unknown variable 'keyring_file_data={path}/keyring'

ANALYSIS
========
From MySQL 5.7.12 onwards, the default --early-plugin-load
value is empty thus we must provide with some nonempty
value to it.

One of the uses of this option is to load the keyring_file
plugin, where we provide some value to it (for e.g.
'keyring_file=keyring_file.so'). However doing so currently
while initializing a datadir is denied! Reason being when
server is invoked for initialization of datadir, the
variable 'bootstrap' in 5.7 (and 'opt_initialize' in trunk)
value is 1. The same is read in plugin_init() in 5.7 [and
in plugin_register_early_plugins() in trunk] and in such a
case we currently skip the registration of early plugins.
As a result of which its not added in the list of plugins
to be loaded early and on encountering this plugin, the
server throws the reported error.

FIX
===
Removed the check for variable 'bootstrap' in 5.7 (and var
'opt_initialize' in trunk) so now registration of early
plugin is done always and hence the loading of plugins etc.
is done as usual.