ewaol-[distro,tests],doc: Change umask to '0027' for ewaol-security

This patch brings the following changes:
 - Sets the umask to '0027' if 'ewaol-security' is in 'DISTRO_FEATURES'.
 - Adds one sub-test that checks if the umask value is correct to
   'user accounts management additional security tests'.
 - Updates the documentation.

Issue-Id: SCM-4415
Signed-off-by: Kamil Dziezyk <kamil.dziezyk@arm.com>
Change-Id: Ibe080bb64aa5edd8cafbe8ac9b940feff94d698e