EQLX: Consolidate CHAP config options

EQLX: Consolidate CHAP config options

In order to reduce configuration option bloat, it would be a good exercise
to consolidate configuration options which many drivers implement under
their own distinct name but have same functionality. Here, a first attempt
is made to consolidate CHAP configuration options. Dell's EQLSanISCSIDriver
is made to use these new set of configuration options 'use_chap_auth',
'chap_username' and 'chap_password' instead of the driver-specific options
'eqlx_use_chap', 'eqlx_chap_login' and 'eqlx_chap_password' respectively in
this patch. More drivers are to be added in the future.

DocImpact: Config options of Dell EQLSanISCSIDriver are changed

Change-Id: I5c51301653ad0f76ce0550e12177ad08f20290e0
Partial-Bug: 1398976