Add support for comments in configuration variables

Add support for comments in configuration variables

This feature will enable the possibility to have many cores
configured in a prox config file, and enable/disable them
through variables.
For instance, a [core $var1] section in a config file will
result in [core 1] if $var1 = 1; the whole section and section
content will be ignored if $var1=#
Before this implementation, [#core 1] or [core #] was already
treated as a commented out section (the whole section was
commented). But there was no way to define a variable $var = #
to comment a section through a variable.

Note that in today's implementation any non numerical
(except s, h, t, -) characteter in the [core] section header
(and not only #) will cause the section to be ignored.
It would probably be better to consider # (as maybe N/A and none)
as comments, and everything else as error. This is however not
supported by the change request.

Change-Id: Id4e2b27a1f9b6d595e0b442dcd971ad44a502031
Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>