Multiple consoles

This CL allows enabling of multiple consoles. A service can be
mapped to a specific console by providing the optional argument,
IE "tty0", to "console" service attribute as follows:

service fbconsole /system/bin/sh
    class core
    console tty0
    disabled
    user shell
    group shell log readproc
    seclabel u:r:shell:s0

Bug: None
Change-Id: I3b24e7f6848bbe5c6475f11334c04ec536e6af88
Tracked-On: https://jira01.devtools.intel.com/browse/BP-289


Signed-off-by: Viorel Suman <viorel.suman@intel.com>